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• MVVM - how to make creating viewmodels at runtime less painfull

  - by Mr Happy

  I apologize for the long question, it reads a bit as a rant, but I promise it's not! I've summarized my question(s) below In the MVC world, things are straightforward. The Model has state, the View shows the Model, and the Controller does stuff to/with the Model (basically), a controller has no state. To do stuff the Controller has some dependencies on web services, repository, the lot. When you instantiate a controller you care about supplying those dependencies, nothing else. When you execute an action (method on Controller), you use those dependencies to retrieve or update the Model or calling some other domain service. If there's any context, say like some user wants to see the details of a particular item, you pass the Id of that item as parameter to the Action. Nowhere in the Controller is there any reference to any state. So far so good. Enter MVVM. I love WPF, I love data binding. I love frameworks that make data binding to ViewModels even easier (using Caliburn Micro a.t.m.). I feel things are less straightforward in this world though. Let's do the exercise again: the Model has state, the View shows the ViewModel, and the ViewModel does stuff to/with the Model (basically), a ViewModel does have state! (to clarify; maybe it delegates all the properties to one or more Models, but that means it must have a reference to the model one way or another, which is state in itself) To do stuff the ViewModel has some dependencies on web services, repository, the lot. When you instantiate a ViewModel you care about supplying those dependencies, but also the state. And this, ladies and gentlemen, annoys me to no end. Whenever you need to instantiate a ProductDetailsViewModel from the ProductSearchViewModel (from which you called the ProductSearchWebService which in turn returned IEnumerable<ProductDTO>, everybody still with me?), you can do one of these things: call new ProductDetailsViewModel(productDTO, _shoppingCartWebService /* dependcy */);, this is bad, imagine 3 more dependencies, this means the ProductSearchViewModel needs to take on those dependencies as well. Also changing the constructor is painfull. call _myInjectedProductDetailsViewModelFactory.Create().Initialize(productDTO);, the factory is just a Func, they are easily generated by most IoC frameworks. I think this is bad because Init methods are a leaky abstraction. You also can't use the readonly keyword for fields that are set in the Init method. I'm sure there are a few more reasons. call _myInjectedProductDetailsViewModelAbstractFactory.Create(productDTO); So... this is the pattern (abstract factory) that is usually recommended for this type of problem. I though it was genious since it satisfies my craving for static typing, until I actually started using it. The amount of boilerplate code is I think too much (you know, apart from the ridiculous variable names I get use). For each ViewModel that needs runtime parameters you'll get two extra files (factory interface and implementation), and you need to type the non-runtime dependencies like 4 extra times. And each time the dependencies change, you get to change it in the factory as well. It feels like I don't even use an DI container anymore. (I think Castle Windsor has some kind of solution for this [with it's own drawbacks, correct me if I'm wrong]). do something with anonymous types or dictionary. I like my static typing. So, yeah. Mixing state and behavior in this way creates a problem which don't exist at all in MVC. And I feel like there currently isn't a really adequate solution for this problem. Now I'd like to observe some things: People actually use MVVM. So they either don't care about all of the above, or they have some brilliant other solution. I haven't found an indepth example of MVVM with WPF. For example, the NDDD-sample project immensely helped me understand some DDD concepts. I'd really like it if someone could point me in the direction of something similar for MVVM/WPF. Maybe I'm doing MVVM all wrong and I should turn my design upside down. Maybe I shouldn't have this problem at all. Well I know other people have asked the same question so I think I'm not the only one. To summarize Am I correct to conclude that having the ViewModel being an integration point for both state and behavior is the reason for some difficulties with the MVVM pattern as a whole? Is using the abstract factory pattern the only/best way to instantiate a ViewModel in a statically typed way? Is there something like an in depth reference implementation available? Is having a lot of ViewModels with both state/behavior a design smell?

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• How customers view and interact with a company

  The Harvard Business Review article written by Rayport and Jaworski is aptly titled “Best Face Forward” because it sheds light on how customers view and interact with a company. In the past most business interaction between customers was performed in a face to face meeting where one party would present an item for sale and then the other would decide whether to purchase the item. In addition, if there was a problem with a purchased item then they would bring the item back to the person who sold the item for resolution. One of my earliest examples of witnessing this was when I was around 6 or 7 years old and I was allowed to spend the summer in Tennessee with my Grandparents. My Grandfather had just written a book about the local history of his town and was selling them to his friends and local bookstores. I still remember he offered to pay me a small commission for every book I helped him sell because I was carrying the books around for him. Every sale he made was face to face with his customers which allowed him to share his excitement for the book with everyone. In today’s modern world there is less and less human interaction as the use of computers and other technologies allow us to communicate within seconds even though both parties may be across the globe or just next door. That being said, customers view a company through multiple access points called faces that represent the ability to interact without actually seeing a human face. As a software engineer this is a good and a bad thing because direct human interaction and technology based interaction have both good and bad attributes based on the customer. How organizations coordinate business and IT functions, to provide quality service varies based on each individual business and the goals and directives put in place by its management. According to Rayport and Jaworski, the type of interaction used through a particular access point may lend itself to be people-dominate, machine-dominate, or a combination of both. The method by which a company communicates information through an access point is a strategic choice that relates costs and customer outcomes. To simplify this, the choice is based on what can give the customer the best experience interacting with the company when the cost of the interaction is also a factor. I personally see examples of this every day at work. The company website is machine-dominate with people updating and maintaining information, our groups department is people dominate because most of the customer interaction is done at the customers location and is backed up by machine based data sources, and our sales/member service department is a hybrid because employees work in tandem with machines in order for them to assist customers with signing up or any other issue they may have. The positive and negative aspects of human and machine interfaces are a key aspect in deciding which interface to use when allowing customers to access a company or a combination of the two. Rayport and Jaworski also used MIT professor Erik Brynjolfsson preliminary catalog of human and machine strengths. He stated that humans outperform machines in judgment, pattern recognition, exception processing, insight, and creativity. I have found this to be true based on the example of how sales and member service reps at my company handle a multitude of questions and various situations with a lot of unknown variables. A machine interface could never effectively be able to handle these scenarios because there are too many variables to consider and would not have the built-in logic to process each customer’s claims and needs. In addition, he also stated that machines outperform humans in collecting, storing, transmitting and routine processing. An example of this would be my employer’s website. Customers can simply go online and purchase a product without even talking to a sales or member services representative. The information is then stored in a database so that the customer can always go back and review there order, and access their selected services. A human, no matter how smart they are would never be able to keep track of hundreds of thousands of customers let alone know what they purchased or how much they paid. In today’s technology driven economy every company must offer their customers multiple methods of accessibly in order to survive. The more of an opportunity a company has to create a positive experience for their customers, in my opinion, they more likely the customer will return to that company again. I have noticed this with my personal shopping habits and experiences. References Rayport, J., & Jaworski, B. (2004). Best Face Forward. Harvard Business Review, 82(12), 47-58. Retrieved from Business Source Complete database.

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• await, WhenAll, WaitAll, oh my!!

  - by cibrax

  If you are dealing with asynchronous work in .NET, you might know that the Task class has become the main driver for wrapping asynchronous calls. Although this class was officially introduced in .NET 4.0, the programming model for consuming tasks was much more simplified in C# 5.0 in .NET 4.5 with the addition of the new async/await keywords. In a nutshell, you can use these keywords to make asynchronous calls as if they were sequential, and avoiding in that way any fork or callback in the code. The compiler takes care of the rest. I was yesterday writing some code for making multiple asynchronous calls to backend services in parallel. The code looked as follow, var allResults = new List<Result>(); foreach(var provider in providers) { var results = await provider.GetResults(); allResults.AddRange(results); } return allResults; You see, I was using the await keyword to make multiple calls in parallel. Something I did not consider was the overhead this code implied after being compiled. I started an interesting discussion with some smart folks in twitter. One of them, Tugberk Ugurlu, had the brilliant idea of actually write some code to make a performance comparison with another approach using Task.WhenAll. There are two additional methods you can use to wait for the results of multiple calls in parallel, WhenAll and WaitAll. WhenAll creates a new task and waits for results in that new task, so it does not block the calling thread. WaitAll, on the other hand, blocks the calling thread. This is the code Tugberk initially wrote, and I modified afterwards to also show the results of WaitAll. class Program { private static Func<Stopwatch, Task>[] funcs = new Func<Stopwatch, Task>[] { async (watch) => { watch.Start(); await Task.Delay(1000); Console.WriteLine("1000 one has been completed."); }, async (watch) => { await Task.Delay(1500); Console.WriteLine("1500 one has been completed."); }, async (watch) => { await Task.Delay(2000); Console.WriteLine("2000 one has been completed."); watch.Stop(); Console.WriteLine(watch.ElapsedMilliseconds + "ms has been elapsed."); } }; static void Main(string[] args) { Console.WriteLine("Await in loop work starts..."); DoWorkAsync().ContinueWith(task => { Console.WriteLine("Parallel work starts..."); DoWorkInParallelAsync().ContinueWith(t => { Console.WriteLine("WaitAll work starts..."); WaitForAll(); }); }); Console.ReadLine(); } static async Task DoWorkAsync() { Stopwatch watch = new Stopwatch(); foreach (var func in funcs) { await func(watch); } } static async Task DoWorkInParallelAsync() { Stopwatch watch = new Stopwatch(); await Task.WhenAll(funcs[0](watch), funcs[1](watch), funcs[2](watch)); } static void WaitForAll() { Stopwatch watch = new Stopwatch(); Task.WaitAll(funcs[0](watch), funcs[1](watch), funcs[2](watch)); } } After running this code, the results were very concluding. Await in loop work starts... 1000 one has been completed. 1500 one has been completed. 2000 one has been completed. 4532ms has been elapsed. Parallel work starts... 1000 one has been completed. 1500 one has been completed. 2000 one has been completed. 2007ms has been elapsed. WaitAll work starts... 1000 one has been completed. 1500 one has been completed. 2000 one has been completed. 2009ms has been elapsed. The await keyword in a loop does not really make the calls in parallel.

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• Myths about Coding Craftsmanship part 2

  - by tom

  Myth 3: The source of all bad code is inept developers and stupid people When you review code is this what you assume?  Shame on you.  You are probably making assumptions in your code if you are assuming so much already.  Bad code can be the result of any number of causes including but not limited to using dated techniques (like boxing when generics are available), not following standards (“look how he does the spacing between arguments!” or “did he really just name that variable ‘bln_Hello_Cats’?”), being redundant, using properties, methods, or objects in a novel way (like switching on button.Text between “Hello World” and “Hello World “ //clever use of space character… sigh), not following the SOLID principals, hacking around assumptions made in earlier iterations / hacking in features that should be worked into the overall design.  The first two issues, while annoying are pretty easy to spot and can be fixed so easily.  If your coding team is made up of experienced professionals who are passionate about staying current then these shouldn’t be happening.  If you work with a variety of skills, backgrounds, and experience then there will be some of this stuff going on.  If you have an opportunity to mentor such a developer who is receptive to constructive criticism don’t be a jerk; help them and the codebase will improve.  A little patience can improve the codebase, your work environment, and even your perspective. The novelty and redundancy I have encountered has often been the use of creativity when language knowledge was perceived as unavailable or too time consuming.  When developers learn on the job you get a lot of this.  Rather than going to MSDN developers will use what they know.  Depending on the constraints of their assignment hacking together what they know may seem quite practical.  This was not stupid though I often wonder how much time is actually “saved” by hacking.  These issues are often harder to untangle if we ever do.  They can also grow out of control as we write hack after hack to make it work and get back to some development that is satisfying. Hacking upon an existing hack is what I call “feeding the monster”.  Code monsters are anti-patterns and hacks gone wild.  The reason code monsters continue to get bigger is that they keep growing in scope, touching more and more of the application.  This is not the result of dumb developers. It is probably the result of avoiding design, not taking the time to understand the problems or anticipate or communicate the vision of the product.  If our developers don’t understand the purpose of a feature or product how do we expect potential customers to do so? Forethought and organization are often what is missing from bad code.  Developers who do not use the SOLID principals should be encouraged to learn these principals and be given guidance on how to apply them.  The time “saved” by giving hackers room to hack will be made up for and then some. Not as technical debt but as shoddy work that if not replaced will be struggled with again and again.  Bad code is not the result of dumb developers (usually) it is the result of trying to do too much without the proper resources and neglecting the right thing that needs doing with the first thoughtless thing that comes into our heads. Object oriented code is all about relationships between objects.  Coders who believe their coworkers are all fools tend to write objects that are difficult to work with, not eager to explain themselves, and perform erratically and irrationally.  If you constantly find you are surrounded by idiots you may want to ask yourself if you are being unreasonable, if you are being closed minded, of if you have chosen the right profession.  Opening your mind up to the idea that you probably work with rational, well-intentioned people will probably make you a better coder and it might even make you less grumpy.  If you are surrounded by jerks who do not engage in the exchange of ideas who do not care about their customers or the durability of the code you are building together then I suggest you find a new place to work.  Myth 4: Customers don’t care about “beautiful” code Craftsmanship is customer focused because it means that the job was done right, the product will withstand the abuse, modifications, and scrutiny of our customers.  Users can appreciate a predictable timeline for a release, a product delivered on time and on budget, a feature set that does not interfere with the task(s) it is supporting, quick turnarounds on exception messages, self healing issues, and less issues.  These are all hindered by skimping on craftsmanship.  When we write data access and when we write reusable code.   What do you think?  Does bad code come primarily from low IQ individuals?  Do customers care about beautiful code?

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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• Thread.Interrupt Is Evil

  - by Alois Kraus

  Recently I have found an interesting issue with Thread.Interrupt during application shutdown. Some application was crashing once a week and we had not really a clue what was the issue. Since it happened not very often it was left as is until we have got some memory dumps during the crash. A memory dump usually means WindDbg which I really like to use (I know I am one of the very few fans of it).  After a quick analysis I did find that the main thread already had exited and the thread with the crash was stuck in a Monitor.Wait. Strange Indeed. Running the application a few thousand times under the debugger would potentially not have shown me what the reason was so I decided to what I call constructive debugging. I did create a simple Console application project and try to simulate the exact circumstances when the crash did happen from the information I have via memory dump and source code reading. The thread that was  crashing was actually MS code from an old version of the Microsoft Caching Application Block. From reading the code I could conclude that the main thread did call the Dispose method on the CacheManger class which did call Thread.Interrupt on the cache scavenger thread which was just waiting for work to do. My first version of the repro looked like this   static void Main(string[] args) { Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); } static void ThreadFunc() { while (true) { object value = Dequeue(); // block until unblocked or awaken via ThreadInterruptedException } } static object WaitObject = new object(); static object Dequeue() { object lret = "got value"; try { lock (WaitObject) { } } catch (ThreadInterruptedException) { Console.WriteLine("Got ThreadInterruptException"); lret = null; } return lret; } I do start a background thread and call Thread.Interrupt on it and then directly let the application terminate. The thread in the meantime does plenty of Monitor.Enter/Leave calls to simulate work on it. This first version did not crash. So I need to dig deeper. From the memory dump I did know that the finalizer thread was doing just some critical finalizers which were closing file handles. Ok lets add some long running finalizers to the sample. class FinalizableObject : CriticalFinalizerObject { ~FinalizableObject() { Console.WriteLine("Hi we are waiting to finalize now and block the finalizer thread for 5s."); Thread.Sleep(5000); } } class Program { static void Main(string[] args) { FinalizableObject fin = new FinalizableObject(); Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); GC.KeepAlive(fin); // prevent finalizing it too early // After leaving main the other thread is woken up via Thread.Abort // while we are finalizing. This causes a stackoverflow in the CLR ThreadAbortException handling at this time. } With this changed Main method and a blocking critical finalizer I did get my crash just like the real application. The funny thing is that this is actually a CLR bug. When the main method is left the CLR does suspend all threads except the finalizer thread and declares all objects as garbage. After the normal finalizers were called the critical finalizers are executed to e.g. free OS handles (usually). Remember that I did call Thread.Interrupt as one of the last methods in the Main method. The Interrupt method is actually asynchronous and does wake a thread up and throws a ThreadInterruptedException only once unlike Thread.Abort which does rethrow the exception when an exception handling clause is left. It seems that the CLR does not expect that a frozen thread does wake up again while the critical finalizers are executed. While trying to raise a ThreadInterrupedException the CLR goes down with an stack overflow. Ups not so nice. Why has this nobody noticed for years is my next question. As it turned out this error does only happen on the CLR for .NET 4.0 (x86 and x64). It does not show up in earlier or later versions of the CLR. I have reported this issue on connect here but so far it was not confirmed as a CLR bug. But I would be surprised if my console application was to blame for a stack overflow in my test thread in a Monitor.Wait call. What is the moral of this story? Thread.Abort is evil but Thread.Interrupt is too. It is so evil that even the CLR of .NET 4.0 contains a race condition during the CLR shutdown. When the CLR gurus can get it wrong the chances are high that you get it wrong too when you use this constructs. If you do not believe me see what Patrick Smacchia does blog about Thread.Abort and List.Sort. Not only the CLR creators can get it wrong. The BCL writers do sometimes have a hard time with correct exception handling as well. If you do tell me that you use Thread.Abort frequently and never had problems with it I do suspect that you do not have looked deep enough into your application to find such sporadic errors.

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• Is Data Science “Science”?

  - by BuckWoody

  I hold the term “science” in very high esteem. I grew up on the Space Coast in Florida, and eventually worked at the Kennedy Space Center, surrounded by very intelligent people who worked in various scientific fields. Recently a new term has entered the computing dialog – “Data Scientist”. Since it’s not a standard term, it has a lot of definitions, and in fact has been disputed as a correct term. After all, the reasoning goes, if there’s no such thing as “Data Science” then how can there be a Data Scientist? This argument has been made before, albeit with a different term – “Computer Science”. In Peter Denning’s excellent article “Is Computer Science Science” (April  2005/Vol. 48, No. 4 COMMUNICATIONS OF THE ACM) there are many points that separate “science” from “engineering” and even “art”.  I won’t repeat the content of that article here (I recommend you read it on your own) but will leverage the points he makes there. Definition of Science To ask the question “is data science ‘science’” then we need to start with a definition of terms. Various references put the definition into the same basic areas: Study of the physical world Systematic and/or disciplined study of a subject area ...and then they include the things studied, the bodies of knowledge and so on. The word itself comes from Latin, and means merely “to know” or “to study to know”. Greek divides knowledge further into “truth” (episteme), and practical use or effects (tekhne). Normally computing falls into the second realm. Definition of Data Science And now a more controversial definition: Data Science. This term is so new and perhaps so niche that the major dictionaries haven’t yet picked it up (my OED reference is older – can’t afford to pop for the online registration at present). Researching the term's general use I created an amalgam of the definitions this way: “Studying and applying mathematical and other techniques to derive information from complex data sets.” Using this definition, data science certainly seems to be science - it's learning about and studying some object or area using systematic methods. But implicit within the definition is the word “application”, which makes the process more akin to engineering or even technology than science. In fact, I find that using these techniques – and data itself – part of science, not science itself. I leave out the concept of studying data patterns or algorithms as part of this discipline. That is actually a domain I see within research, mathematics or computer science. That of course is a type of science, but does not seek for practical applications. As part of the argument against calling it “Data Science”, some point to the scientific method of creating a hypothesis, testing with controls, testing results against the hypothesis, and documenting for repeatability.  These are not steps that we often take in working with data. We normally start with a question, and fit patterns and algorithms to predict outcomes and find correlations. In this way Data Science is more akin to statistics (and in fact makes heavy use of them) in the process rather than starting with an assumption and following on with it. So, is Data Science “Science”? I’m uncertain – and I’m uncertain it matters. Even if we are facing rampant “title inflation” these days (does anyone introduce themselves as a secretary or supervisor anymore?) I can tolerate the term at least from the intent that we use data to study problems across a wide spectrum, rather than restricting it to a single domain. And I also understand those who have worked hard to achieve the very honorable title of “scientist” who have issues with those who borrow the term without asking. What do you think? Science, or not? Does it matter?

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• Code refactoring with Visual Studio 2010 Part-4

  - by Jalpesh P. Vadgama

  I have been writing few post with code refactoring features in Visual Studio 2010. This post also will be part of series and this post will be last of the series. In this post I am going explain two features 1) Encapsulate Field and 2) Extract Interface. Let’s explore both features in details. Encapsulate Field: This is a nice code refactoring feature provides by Visual Studio 2010. With help of this feature we can create properties from the existing private field of the class. Let’s take a simple example of Customer Class. In that I there are two private field called firstName and lastName. Below is the code for the class. public class Customer { private string firstName; private string lastName; public string Address { get; set; } public string City { get; set; } } Now lets encapsulate first field firstName with Encapsulate feature. So first select that field and goto refactor menu in Visual Studio 2010 and click on Encapsulate Field. Once you click that a dialog box will appear like following. Now once you click OK a preview dialog box will open as we have selected preview reference changes. I think its a good options to check that option to preview code that is being changed by IDE itself. Dialog will look like following. Once you click apply it create a new property called FirstName. Same way I have done for the lastName and now my customer class code look like following. public class Customer { private string firstName; public string FirstName { get { return firstName; } set { firstName = value; } } private string lastName; public string LastName { get { return lastName; } set { lastName = value; } } public string Address { get; set; } public string City { get; set; } } So you can see that its very easy to create properties with existing fields and you don’t have to change anything there in code it will change all the stuff itself. Extract Interface: When you are writing software prototype and You don’t know the future implementation of that then its a good practice to use interface there. I am going to explain here that How we can extract interface from the existing code without writing a single line of code with the help of code refactoring feature of Visual Studio 2010. For that I have create a Simple Repository class called CustomerRepository with three methods like following. public class CustomerRespository { public void Add() { // Some code to add customer } public void Update() { //some code to update customer } public void Delete() { //some code delete customer } } In above class there are three method Add,Update and Delete where we are going to implement some code for each one. Now I want to create a interface which I can use for my other entities in project. So let’s create a interface from the above class with the help of Visual Studio 2010. So first select class and goto refactor menu and click Extract Interface. It will open up dialog box like following. Here I have selected all the method for interface and Once I click OK then it will create a new file called ICustomerRespository where it has created a interface. Just like following. Here is a code for that interface. using System; namespace CodeRefractoring { interface ICustomerRespository { void Add(); void Delete(); void Update(); } } Now let's see the code for the our class. It will also changed like following to implement the interface. public class CustomerRespository : ICustomerRespository { public void Add() { // Some code to add customer } public void Update() { //some code to update customer } public void Delete() { //some code delete customer } } Isn't that great we have created a interface and implemented it without writing a single line of code. Hope you liked it. Stay tuned for more.. Till that Happy Programming.

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• Breaking 1NF to model subset constraints. Does this sound sane?

  - by Chris Travers

  My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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• Upgrading to Code Based Migrations EF 4.3.1 with Connector/Net 6.6

  - by GABMARTINEZ

  Entity Framework 4.3.1 includes a new feature called code first migrations.  We are adding support for this feature in our upcoming 6.6 release of Connector/Net.  In this walk-through we'll see the workflow of code-based migrations when you have an existing application and you would like to upgrade to this EF 4.3.1 version and use this approach, so you can keep track of the changes that you do to your database.   The first thing we need to do is add the new Entity Framework 4.3.1 package to our application. This should via the NuGet package manager.  You can read more about why EF is not part of the .NET framework here. Adding EF 4.3.1 to our existing application  Inside VS 2010 go to Tools -> Library Package Manager -> Package Manager Console, this will open the Power Shell Host Window where we can work with all the EF commands. In order to install this library to your existing application you should type Install-Package EntityFramework This will make some changes to your application. So Let's check them. In your .config file you'll see a  <configSections> which contains the version you have from EntityFramework and also was added the <entityFramework> section as shown below. This section is by default configured to use SQL Express which won't be necesary for this case. So you can comment it out or leave it empty. Also please make sure you're using the Connector/Net 6.6.x version which is the one that has this support as is shown in the previous image. At this point we face one issue; in order to be able to work with Migrations we need the __MigrationHistory table that we don't have yet since our Database was created with an older version. This table is used to keep track of the changes in our model. So we need to get it in our existing Database. Getting a Migration-History table into an existing database First thing we need to do to enable migrations in our existing application is to create our configuration class which will set up the MySqlClient Provider as our SQL Generator. So we have to add it with the following code: using System.Data.Entity.Migrations;     //add this at the top of your cs file public class Configuration : DbMigrationsConfiguration<NameOfYourDbContext>  //Make sure to use the name of your existing DBContext { public Configuration() { this.AutomaticMigrationsEnabled = false; //Set Automatic migrations to false since we'll be applying the migrations manually for this case. SetSqlGenerator("MySql.Data.MySqlClient", new MySql.Data.Entity.MySqlMigrationSqlGenerator());     }   }  This code will set up our configuration that we'll be using when executing all the migrations for our application. Once we have done this we can Build our application so we can check that everything is fine. Creating our Initial Migration Now let's add our Initial Migration. In Package Manager Console, execute "add-migration InitialCreate", you can use any other name but I like to set this as our initial create for future reference. After we run this command, some changes were done in our application: A new Migrations Folder was created. A new class migration call InitialCreate which in most of the cases should have empty Up and Down methods as long as your database is up to date with your Model. Since all your entities already exists, delete all duplicated code to create any entity which exists already in your Database if there is any. I found this easier when you don't have any pending updates to do to your database. Now we have our empty migration that will make no changes in our database and represents how are all the things at the begining of our migrations.  Finally, let's create our MigrationsHistory table. Optionally you can add SQL code to delete the edmdata table which is not needed anymore. public override void Up() { // Just make sure that you used 4.1 or later version         Sql("DROP TABLE EdmMetadata"); } From our Package Manager Console let's type: Update-database; If you like to see the operations made on each Update-database command you can use the flag -verbose after the Update-database. This will make two important changes.  It will execute the Up method in the initial migration which has no changes in the database. And second, and very important,  it will create the __MigrationHistory table necessary to keep track of your changes. And next time you make a change to your database it will compare the current model to the one stored in the Model Column of this table. Conclusion The important thing of this walk through is that we must create our initial migration before we start doing any changes to our model. This way we'll be adding the necessary __MigrationsHistory table to our existing database, so we can keep our database up to date with all the changes we do in our context model using migrations. Hope you have found this information useful. Please let us know if you have any questions or comments, also please check our forums here where we keep answering questions in general for the community.  Happy MySQL/Net Coding!

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• Webcor Builders Coordinates Construction Schedules and Mitigates Potential Delays More Efficiently with Integrated Project Management

  - by Sylvie MacKenzie, PMP

  Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";} With more than 40 years of commercial construction experience, Webcor Builders is a leading builder of distinguished, high-profile projects, including high-rise condominiums and hotels, laboratories, healthcare centers, and public works projects. Webcor is also known for its award-winning concrete, interior construction, historic restoration, and seismic renovation work. The company has completed more than 50 million square feet of projects to date. Considering the variety and complexity of the construction projects Webcor undertakes, an integrated project management solution is critical to ensuring optimal efficiency and completing client projects on time and on budget. The company previously used a number of scheduling systems for its various building projects. These packages provided different levels of schedule detail and required schedulers, engineers, and other employees to learn multiple systems. From an IT cost and complexity perspective, the company had to manage multiple scheduling systems and pay for multiple sets of licenses. The company looked to standardize on an enterprise project management system, and selected Oracle’s Primavera P6 Enterprise Project Portfolio Management. Webcor uses the solution’s advanced capabilities to schedule complex projects, analyze delays, model and propose multiple scenarios to demonstrate and mitigate delays and cost overruns, and process that information efficiently to deliver the scheduling precision that public and private projects require. In fact, the solution was instrumental in helping the company’s expansion into public sector projects during the recent economic downturn, and with Primavera P6 in place, it can deliver the precise schedule reporting required for large public projects. With Primavera P6 in place, the company could deliver the precise scheduling and milestone reporting capabilities required for large public projects. The solution is in managing the high-profile University of California – Berkeley Memorial Stadium project. Webcor was hired as construction manager and general contractor for the stadium renovation project, which is a fast-paced project located near the seismically active Hayward Fault Zone. Due to the University of California’s football schedule, meeting the Universities deadline for the coming season placed Webcor in a situation where risk awareness and early warnings of issues would be paramount. Webcor and the extended project team needed a solution that could instantly analyze alternate scenarios to mitigate potential delays; Primavera would deliver those answers.The team would also need to enable multiple stakeholders to use an internet-based platform to access the schedule from various locations, and model complicated sequencing requirements where swift decisions would be made to keep the project on track. The schedule is an integral part of Webcor’s construction management process for the stadium project. Rather than providing the client with the industry-standard monthly update, Webcor updates the critical path method (CPM) schedule on a weekly basis. The project team also reviews the schedule and updates weekly to confirm that progress and forecasted performance are accurate. Hired by the University for their ability to deliver in high risk environments The Webcor team was hit recently with a design supplement that could have added up to 70 days to the project. Using Oracle Primavera P6 the team sprung into action analyzing multiple “what if” scenarios to review mitigation means and methods.  Determined to make sure the Bears could take the field in the coming season the project team nearly eliminated the impact with their creative analysis in working the schedule. The total time from the issuance of the final design supplement to an agreed mitigation response was less than one week; leveraging the Oracle Primavera solution Webcor was able to deliver superior customer value With the ability to efficiently manage projects and schedules, Webcor can ensure it completes its projects on time and on budget, as well as inform clients about what changes to plans will mean in terms of delays and additional costs. Read the complete customer case study at :  http://www.oracle.com/us/corporate/customers/customersearch/webcor-builders-1-primavera-ss-1639886.html

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• Rebuilding CoasterBuzz, Part II: Hot data objects

  - by Jeff

  This is the second post, originally from my personal blog, in a series about rebuilding one of my Web sites, which has been around for 12 years. More: Part I: Evolution, and death to WCF After the rush to get moving on stuff, I temporarily lost interest. I went almost two weeks without touching the project, in part because the next thing on my backlog was doing up a bunch of administrative pages. So boring. Unfortunately, because most of the site's content is user-generated, you need some facilities for editing data. CoasterBuzz has a database full of amusement parks and roller coasters. The entities enjoy the relationships that you would expect, though they're further defined by "instances" of a coaster, to define one that has moved between parks as one, with different names and operational dates. And of course, there are pictures and news items, too. It's not horribly complex, except when you have to account for a name change and display just the newest name. In all previous versions, data access was straight SQL. As so much of the old code was rooted in 2003, with some changes in 2008, there wasn't much in the way of ORM frameworks going on then. Let me rephrase that, I mostly wasn't interested in ORM's. Since that time, I used a little LINQ to SQL in some projects, and a whole bunch of nHibernate while at Microsoft. Through all of that experience, I have to admit that these frameworks are often a bigger pain in the ass than not. They're great for basic crud operations, but when you start having all kinds of exotic relationships, they get difficult, and generate all kinds of weird SQL under the covers. The black box can quickly turn into a black hole. Sometimes you end up having to build all kinds of new expertise to do things "right" with a framework. Still, despite my reservations, I used the newer version of Entity Framework, with the "code first" modeling, in a science project and I really liked it. Since it's just a right-click away with NuGet, I figured I'd give it a shot here. My initial effort was spent defining the context class, which requires a bit of work because I deviate quite a bit from the conventions that EF uses, starting with table names. Then throw some partial querying of certain tables (where you'll find image data), and you're splitting tables across several objects (navigation properties). I won't go into the details, because these are all things that are well documented around the Internet, but there was a minor learning curve there. The basics of reading data using EF are fantastic. For example, a roller coaster object has a park associated with it, as well as a number of instances (if it was ever relocated), and there also might be a big banner image for it. This is stupid easy to use because it takes one line of code in your repository class, and by the time you pass it to the view, you have a rich object graph that has everything you need to display stuff. Likewise, editing simple data is also, well, simple. For this goodness, thank the ASP.NET MVC framework. The UpdateModel() method on the controllers is very elegant. Remember the old days of assigning all kinds of properties to objects in your Webforms code-behind? What a time consuming mess that used to be. Even if you're not using an ORM tool, having hydrated objects come off the wire is such a time saver. Not everything is easy, though. When you have to persist a complex graph of objects, particularly if they were composed in the user interface with all kinds of AJAX elements and list boxes, it's not just a simple matter of submitting the form. There were a few instances where I ended up going back to "old-fashioned" SQL just in the interest of time. It's not that I couldn't do what I needed with EF, it's just that the efficiency, both my own and that of the generated SQL, wasn't good. Since EF context objects expose a database connection object, you can use that to do the old school ADO.NET stuff you've done for a decade. Using various extension methods from POP Forums' data project, it was a breeze. You just have to stick to your decision, in this case. When you start messing with SQL directly, you can't go back in the same code to messing with entities because EF doesn't know what you're changing. Not really a big deal. There are a number of take-aways from using EF. The first is that you write a lot less code, which has always been a desired outcome of ORM's. The other lesson, and I particularly learned this the hard way working on the MSDN forums back in the day, is that trying to retrofit an ORM framework into an existing schema isn't fun at all. The CoasterBuzz database isn't bad, but there are design decisions I'd make differently if I were starting from scratch. Now that I have some of this stuff done, I feel like I can start to move on to the more interesting things on the backlog. There's a lot to do, but at least it's fun stuff, and not more forms that will be used infrequently.

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• Rebuilding CoasterBuzz, Part IV: Dependency injection, it's what's for breakfast

  - by Jeff

  (Repost from my personal blog.) This is another post in a series about rebuilding one of my Web sites, which has been around for 12 years. I hope to relaunch soon. More: Part I: Evolution, and death to WCF Part II: Hot data objects Part III: The architecture using the "Web stack of love" If anything generally good for the craft has come out of the rise of ASP.NET MVC, it's that people are more likely to use dependency injection, and loosely couple the pieces parts of their applications. A lot of the emphasis on coding this way has been to facilitate unit testing, and that's awesome. Unit testing makes me feel a lot less like a hack, and a lot more confident in what I'm doing. Dependency injection is pretty straight forward. It says, "Given an instance of this class, I need instances of other classes, defined not by their concrete implementations, but their interfaces." Probably the first place a developer exercises this in when having a class talk to some kind of data repository. For a very simple example, pretend the FooService has to get some Foo. It looks like this: public class FooService {    public FooService(IFooRepository fooRepo)    {       _fooRepo = fooRepo;    }    private readonly IFooRepository _fooRepo;    public Foo GetMeFoo()    {       return _fooRepo.FooFromDatabase();    } } When we need the FooService, we ask the dependency container to get it for us. It says, "You'll need an IFooRepository in that, so let me see what that's mapped to, and put it in there for you." Why is this good for you? It's good because your FooService doesn't know or care about how you get some foo. You can stub out what the methods and properties on a fake IFooRepository might return, and test just the FooService. I don't want to get too far into unit testing, but it's the most commonly cited reason to use DI containers in MVC. What I wanted to mention is how there's another benefit in a project like mine, where I have to glue together a bunch of stuff. For example, when I have someone sign up for a new account on CoasterBuzz, I'm actually using POP Forums' new account mailer, which composes a bunch of text that includes a link to verify your account. The thing is, I want to use custom text and some other logic that's specific to CoasterBuzz. To accomplish this, I make a new class that inherits from the forum's NewAccountMailer, and override some stuff. Easy enough. Then I use Ninject, the DI container I'm using, to unbind the forum's implementation, and substitute my own. Ninject uses something called a NinjectModule to bind interfaces to concrete implementations. The forum has its own module, and then the CoasterBuzz module is loaded second. The CB module has two lines of code to swap out the mailer implementation: Unbind<PopForums.Email.INewAccountMailer>(); Bind<PopForums.Email.INewAccountMailer>().To<CbNewAccountMailer>(); Piece of cake! Now, when code asks the DI container for an INewAccountMailer, it gets my custom implementation instead. This is a lot easier to deal with than some of the alternatives. I could do some copy-paste, but then I'm not using well-tested code from the forum. I could write stuff from scratch, but then I'm throwing away a bunch of logic I've already written (in this case, stuff around e-mail, e-mail settings, mail delivery failures). There are other places where the DI container comes in handy. For example, CoasterBuzz does a number of custom things with user profiles, and special content for paid members. It uses the forum as the core piece to managing users, so I can ask the container to get me instances of classes that do user lookups, for example, and have zero care about how the forum handles database calls, configuration, etc. What a great world to live in, compared to ten years ago. Sure, the primary interest in DI is around the "separation of concerns" and facilitating unit testing, but as your library grows and you use more open source, it starts to be the glue that pulls everything together.

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• Optimizing a thread safe Java NIO / Serialization / FIFO Queue [migrated]

  - by trialcodr

  I've written a thread safe, persistent FIFO for Serializable items. The reason for reinventing the wheel is that we simply can't afford any third party dependencies in this project and want to keep this really simple. The problem is it isn't fast enough. Most of it is undoubtedly due to reading and writing directly to disk but I think we should be able to squeeze a bit more out of it anyway. Any ideas on how to improve the performance of the 'take'- and 'add'-methods? /** * <code>DiskQueue</code> Persistent, thread safe FIFO queue for * <code>Serializable</code> items. */ public class DiskQueue<ItemT extends Serializable> { public static final int EMPTY_OFFS = -1; public static final int LONG_SIZE = 8; public static final int HEADER_SIZE = LONG_SIZE * 2; private InputStream inputStream; private OutputStream outputStream; private RandomAccessFile file; private FileChannel channel; private long offs = EMPTY_OFFS; private long size = 0; public DiskQueue(String filename) { try { boolean fileExists = new File(filename).exists(); file = new RandomAccessFile(filename, "rwd"); if (fileExists) { size = file.readLong(); offs = file.readLong(); } else { file.writeLong(size); file.writeLong(offs); } } catch (FileNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } channel = file.getChannel(); inputStream = Channels.newInputStream(channel); outputStream = Channels.newOutputStream(channel); } /** * Add item to end of queue. */ public void add(ItemT item) { try { synchronized (this) { channel.position(channel.size()); ObjectOutputStream s = new ObjectOutputStream(outputStream); s.writeObject(item); s.flush(); size++; file.seek(0); file.writeLong(size); if (offs == EMPTY_OFFS) { offs = HEADER_SIZE; file.writeLong(offs); } notify(); } } catch (IOException e) { throw new RuntimeException(e); } } /** * Clears overhead by moving the remaining items up and shortening the file. */ public synchronized void defrag() { if (offs > HEADER_SIZE && size > 0) { try { long totalBytes = channel.size() - offs; ByteBuffer buffer = ByteBuffer.allocateDirect((int) totalBytes); channel.position(offs); for (int bytes = 0; bytes < totalBytes;) { int res = channel.read(buffer); if (res == -1) { throw new IOException("Failed to read data into buffer"); } bytes += res; } channel.position(HEADER_SIZE); buffer.flip(); for (int bytes = 0; bytes < totalBytes;) { int res = channel.write(buffer); if (res == -1) { throw new IOException("Failed to write buffer to file"); } bytes += res; } offs = HEADER_SIZE; file.seek(LONG_SIZE); file.writeLong(offs); file.setLength(HEADER_SIZE + totalBytes); } catch (IOException e) { throw new RuntimeException(e); } } } /** * Returns the queue overhead in bytes. */ public synchronized long overhead() { return (offs == EMPTY_OFFS) ? 0 : offs - HEADER_SIZE; } /** * Returns the first item in the queue, blocks if queue is empty. */ public ItemT peek() throws InterruptedException { block(); synchronized (this) { if (offs != EMPTY_OFFS) { return readItem(); } } return peek(); } /** * Returns the number of remaining items in queue. */ public synchronized long size() { return size; } /** * Removes and returns the first item in the queue, blocks if queue is empty. */ public ItemT take() throws InterruptedException { block(); try { synchronized (this) { if (offs != EMPTY_OFFS) { ItemT result = readItem(); size--; offs = channel.position(); file.seek(0); if (offs == channel.size()) { truncate(); } file.writeLong(size); file.writeLong(offs); return result; } } return take(); } catch (IOException e) { throw new RuntimeException(e); } } /** * Throw away all items and reset the file. */ public synchronized void truncate() { try { offs = EMPTY_OFFS; file.setLength(HEADER_SIZE); size = 0; } catch (IOException e) { throw new RuntimeException(e); } } /** * Block until an item is available. */ protected void block() throws InterruptedException { while (offs == EMPTY_OFFS) { try { synchronized (this) { wait(); file.seek(LONG_SIZE); offs = file.readLong(); } } catch (IOException e) { throw new RuntimeException(e); } } } /** * Read and return item. */ @SuppressWarnings("unchecked") protected ItemT readItem() { try { channel.position(offs); return (ItemT) new ObjectInputStream(inputStream).readObject(); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } } }

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• Performance triage

  - by Dave

  Folks often ask me how to approach a suspected performance issue. My personal strategy is informed by the fact that I work on concurrency issues. (When you have a hammer everything looks like a nail, but I'll try to keep this general). A good starting point is to ask yourself if the observed performance matches your expectations. Expectations might be derived from known system performance limits, prototypes, and other software or environments that are comparable to your particular system-under-test. Some simple comparisons and microbenchmarks can be useful at this stage. It's also useful to write some very simple programs to validate some of the reported or expected system limits. Can that disk controller really tolerate and sustain 500 reads per second? To reduce the number of confounding factors it's better to try to answer that question with a very simple targeted program. And finally, nothing beats having familiarity with the technologies that underlying your particular layer. On the topic of confounding factors, as our technology stacks become deeper and less transparent, we often find our own technology working against us in some unexpected way to choke performance rather than simply running into some fundamental system limit. A good example is the warm-up time needed by just-in-time compilers in Java Virtual Machines. I won't delve too far into that particular hole except to say that it's rare to find good benchmarks and methodology for java code. Another example is power management on x86. Power management is great, but it can take a while for the CPUs to throttle up from low(er) frequencies to full throttle. And while I love "turbo" mode, it makes benchmarking applications with multiple threads a chore as you have to remember to turn it off and then back on otherwise short single-threaded runs may look abnormally fast compared to runs with higher thread counts. In general for performance characterization I disable turbo mode and fix the power governor at "performance" state. Another source of complexity is the scheduler, which I've discussed in prior blog entries. Lets say I have a running application and I want to better understand its behavior and performance. We'll presume it's warmed up, is under load, and is an execution mode representative of what we think the norm would be. It should be in steady-state, if a steady-state mode even exists. On Solaris the very first thing I'll do is take a set of "pstack" samples. Pstack briefly stops the process and walks each of the stacks, reporting symbolic information (if available) for each frame. For Java, pstack has been augmented to understand java frames, and even report inlining. A few pstack samples can provide powerful insight into what's actually going on inside the program. You'll be able to see calling patterns, which threads are blocked on what system calls or synchronization constructs, memory allocation, etc. If your code is CPU-bound then you'll get a good sense where the cycles are being spent. (I should caution that normal C/C++ inlining can diffuse an otherwise "hot" method into other methods. This is a rare instance where pstack sampling might not immediately point to the key problem). At this point you'll need to reconcile what you're seeing with pstack and your mental model of what you think the program should be doing. They're often rather different. And generally if there's a key performance issue, you'll spot it with a moderate number of samples. I'll also use OS-level observability tools to lock for the existence of bottlenecks where threads contend for locks; other situations where threads are blocked; and the distribution of threads over the system. On Solaris some good tools are mpstat and too a lesser degree, vmstat. Try running "mpstat -a 5" in one window while the application program runs concurrently. One key measure is the voluntary context switch rate "vctx" or "csw" which reflects threads descheduling themselves. It's also good to look at the user; system; and idle CPU percentages. This can give a broad but useful understanding if your threads are mostly parked or mostly running. For instance if your program makes heavy use of malloc/free, then it might be the case you're contending on the central malloc lock in the default allocator. In that case you'd see malloc calling lock in the stack traces, observe a high csw/vctx rate as threads block for the malloc lock, and your "usr" time would be less than expected. Solaris dtrace is a wonderful and invaluable performance tool as well, but in a sense you have to frame and articulate a meaningful and specific question to get a useful answer, so I tend not to use it for first-order screening of problems. It's also most effective for OS and software-level performance issues as opposed to HW-level issues. For that reason I recommend mpstat & pstack as my the 1st step in performance triage. If some other OS-level issue is evident then it's good to switch to dtrace to drill more deeply into the problem. Only after I've ruled out OS-level issues do I switch to using hardware performance counters to look for architectural impediments.

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• ADF Business Components

  - by Arda Eralp

  ADF Business Components and JDeveloper simplify the development, delivery, and customization of business applications for the Java EE platform. With ADF Business Components, developers aren't required to write the application infrastructure code required by the typical Java EE application to: Connect to the database Retrieve data Lock database records Manage transactions   ADF Business Components addresses these tasks through its library of reusable software components and through the supporting design time facilities in JDeveloper. Most importantly, developers save time using ADF Business Components since the JDeveloper design time makes typical development tasks entirely declarative. In particular, JDeveloper supports declarative development with ADF Business Components to: Author and test business logic in components which automatically integrate with databases Reuse business logic through multiple SQL-based views of data, supporting different application tasks Access and update the views from browser, desktop, mobile, and web service clients Customize application functionality in layers without requiring modification of the delivered application The goal of ADF Business Components is to make the business services developer more productive.   ADF Business Components provides a foundation of Java classes that allow your business-tier application components to leverage the functionality provided in the following areas: Simplifying Data Access Design a data model for client displays, including only necessary data Include master-detail hierarchies of any complexity as part of the data model Implement end-user Query-by-Example data filtering without code Automatically coordinate data model changes with business services layer Automatically validate and save any changes to the database   Enforcing Business Domain Validation and Business Logic Declaratively enforce required fields, primary key uniqueness, data precision-scale, and foreign key references Easily capture and enforce both simple and complex business rules, programmatically or declaratively, with multilevel validation support Navigate relationships between business domain objects and enforce constraints related to compound components   Supporting Sophisticated UIs with Multipage Units of Work Automatically reflect changes made by business service application logic in the user interface Retrieve reference information from related tables, and automatically maintain the information when the user changes foreign-key values Simplify multistep web-based business transactions with automatic web-tier state management Handle images, video, sound, and documents without having to use code Synchronize pending data changes across multiple views of data Consistently apply prompts, tooltips, format masks, and error messages in any application Define custom metadata for any business components to support metadata-driven user interface or application functionality Add dynamic attributes at runtime to simplify per-row state management   Implementing High-Performance Service-Oriented Architecture Support highly functional web service interfaces for business integration without writing code Enforce best-practice interface-based programming style Simplify application security with automatic JAAS integration and audit maintenance "Write once, run anywhere": use the same business service as plain Java class, EJB session bean, or web service   Streamlining Application Customization Extend component functionality after delivery without modifying source code Globally substitute delivered components with extended ones without modifying the application   ADF Business Components implements the business service through the following set of cooperating components: Entity object An entity object represents a row in a database table and simplifies modifying its data by handling all data manipulation language (DML) operations for you. These are basically your 1 to 1 representation of a database table. Each table in the database will have 1 and only 1 EO. The EO contains the mapping between columns and attributes. EO's also contain the business logic and validation. These are you core data services. They are responsible for updating, inserting and deleting records. The Attributes tab displays the actual mapping between attributes and columns, the mapping has following fields: Name : contains the name of the attribute we expose in our data model. Type : defines the data type of the attribute in our application. Column : specifies the column to which we want to map the attribute with Column Type : contains the type of the column in the database   View object A view object represents a SQL query. You use the full power of the familiar SQL language to join, filter, sort, and aggregate data into exactly the shape required by the end-user task. The attributes in the View Objects are actually coming from the Entity Object. In the end the VO will generate a query but you basically build a VO by selecting which EO need to participate in the VO and which attributes of those EO you want to use. That's why you have the Entity Usage column so you can see the relation between VO and EO. In the query tab you can clearly see the query that will be generated for the VO. At this stage we don't need it and just use it for information purpose. In later stages we might use it. Application module An application module is the controller of your data layer. It is responsible for keeping hold of the transaction. It exposes the data model to the view layer. You expose the VO's through the Application Module. This is the abstraction of your data layer which you want to show to the outside word.It defines an updatable data model and top-level procedures and functions (called service methods) related to a logical unit of work related to an end-user task. While the base components handle all the common cases through built-in behavior, customization is always possible and the default behavior provided by the base components can be easily overridden or augmented. When you create EO's, a foreign key will be translated into an association in our model. It defines the type of relation and who is the master and child as well as how the visibility of the association looks like. A similar concept exists to identify relations between view objects. These are called view links. These are almost identical as association except that a view link is based upon attributes defined in the view object. It can also be based upon an association. Here's a short summary: Entity Objects: representations of tables Association: Relations between EO's. Representations of foreign keys View Objects: Logical model View Links: Relationships between view objects Application Model: interface to your application  

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• How to break out of if statement

  - by TheBroodian

  I'm not sure if the title is exactly an accurate representation of what I'm actually trying to ask, but that was the best I could think of. I am experiencing an issue with my character class. I have developed a system so that he can perform chain attacks, and something that was important to me was that 1)button presses during the process of an attack wouldn't interrupt the character, and 2) at the same time, button presses should be stored so that the player can smoothly queue up chain attacks in the middle of one so that gameplay doesn't feel rigid or unresponsive. This all begins when the player presses the punch button. Upon pressing the punch button, the game checks the state of the dpad at the moment of the button press, and then translates the resulting combined buttons into an int which I use as an enumerator relating to a punch method for the character. The enumerator is placed into a List so that the next time the character's Update() method is called, it will execute the next punch in the list. It only executes the next punch if my character is flagged with acceptInput as true. All attacks flag acceptInput as false, to prevent the interruption of attacks, and then at the end of an attack, acceptInput is set back to true. While accepting input, all other actions are polled for, i.e. jumping, running, etc. In runtime, if I attack, and then queue up another attack behind it (by pressing forward+punch) I can see the second attack visibly execute, which should flag acceptInput as false, yet it gets interrupted and my character will stop punching and start running if I am still holding down the dpad. Included is some code for context. This is the input region for my character. //Placed this outside the if (acceptInput) tree because I want it //to be taken into account whether we are accepting input or not. //This will queue up attacks, which will only be executed if we are accepting input. //This creates a desired effect that helps control the character in a // smoother fashion for the player. if (Input.justPressed(buttonManager.Punch)) { int dpadPressed = Input.DpadState(0); if (attackBuffer.Count() < 1) { attackBuffer.Add(CheckPunch(dpadPressed)); } else { attackBuffer.Clear(); attackBuffer.Add(CheckPunch(dpadPressed)); } } if (acceptInput) { if (attackBuffer.Count() > 0) { ExecutePunch(attackBuffer[0]); attackBuffer.RemoveAt(0); } //If D-Pad left is being held down. if (Input.DpadDirectionHeld(0, buttonManager.Left)) { flipped = false; if (onGround) { newAnimation = "run"; } velocity = new Vector2(velocity.X - acceleration, velocity.Y); if (walking == true && velocity.X <= -walkSpeed) { velocity.X = -walkSpeed; } else if (walking == false && velocity.X <= -maxSpeed) { velocity.X = -maxSpeed; } } //If D-Pad right is being held down. if (Input.DpadDirectionHeld(0, buttonManager.Right)) { flipped = true; if (onGround) { newAnimation = "run"; } velocity = new Vector2(velocity.X + acceleration, velocity.Y); if (walking == true && velocity.X >= walkSpeed) { velocity.X = walkSpeed; } else if (walking == false && velocity.X >= maxSpeed) { velocity.X = maxSpeed; } } //If jump/accept button is pressed. if (Input.justPressed(buttonManager.JumpAccept)) { if (onGround) { Jump(); } } //If toggle element next button is pressed. if (Input.justPressed(buttonManager.ToggleElementNext)) { if (elements.Count != 0) { elementInUse++; if (elementInUse >= elements.Count) { elementInUse = 0; } } } //If toggle element last button is pressed. if (Input.justPressed(buttonManager.ToggleElementLast)) { if (elements.Count != 0) { elementInUse--; if (elementInUse < 0) { elementInUse = Convert.ToSByte(elements.Count() - 1); } } } //If character is in the process of jumping. if (jumping == true) { if (Input.heldDown(buttonManager.JumpAccept)) { velocity.Y -= fallSpeed.Y; maxJumpTime -= elapsed; } if (Input.justReleased(buttonManager.JumpAccept) || maxJumpTime <= 0) { jumping = false; maxJumpTime = 0; } } //Won't execute abilities if input isn't being accepted. foreach (PlayerAbility ability in playerAbilities) { if (buffer.Matches(ability)) { if (onGround) { ability.Activate(); } if (!onGround && ability.UsableInAir) { ability.Activate(); } else if (!onGround && !ability.UsableInAir) { buffer.Clear(); } } } } When the attackBuffer calls ExecutePunch(int) method, ExecutePunch() will call one of the following methods: private void NeutralPunch1() //0 { acceptInput = false; busy = true; newAnimation = "punch1"; numberOfAttacks++; timeSinceLastAttack = 0; } private void ForwardPunch2(bool toLeft) //true == 7, false == 4 { forwardPunch2Timer = 0f; acceptInput = false; busy = true; newAnimation = "punch2begin"; numberOfAttacks++; timeSinceLastAttack = 0; if (toLeft) { velocity.X -= 800; } if (!toLeft) { velocity.X += 800; } } I assume the attack is being interrupted due to the fact that ExecutePunch() is in the same if statement as running, but I haven't been able to find a suitable way to stop this happening. Thank you ahead of time for reading this, I apologize for it having become so long winded.

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• Multiple enemy array in LibGDX

  - by johnny-b

  I am trying to make a multiple enemy array, where every 30 secods a new bullet comes from a random point. And if the bullet is clicked it should disapear and a pop like an explosion should appear. And if the bullet hits the ball then the ball pops. so the bullet should change to a different sprite or texture. same with the ball pop. But all that happens is the bullet if touched pops and nothing else happens. And if modified then the bullet keeps flashing as the update is way too much. I have added COMMENTS in the code to explain more on the issues. below is the code. if more code is needed i will provide. Thank you public class GameRenderer { private GameWorld myWorld; private OrthographicCamera cam; private ShapeRenderer shapeRenderer; private SpriteBatch batcher; // Game Objects private Ball ball; private ScrollHandler scroller; private Background background; private Bullet bullet1; private BulletPop bPop; private Array<Bullet> bullets; // This is for the delay of the bullet coming one by one every 30 seconds. /** The time of the last shot fired, we set it to the current time in nano when the object is first created */ double lastShot = TimeUtils.nanoTime(); /** Convert 30 seconds into nano seconds, so 30,000 milli = 30 seconds */ double shotFreq = TimeUtils.millisToNanos(30000); // Game Assets private TextureRegion bg, bPop; private Animation bulletAnimation, ballAnimation; private Animation ballPopAnimation; public GameRenderer(GameWorld world) { myWorld = world; cam = new OrthographicCamera(); cam.setToOrtho(true, 480, 320); batcher = new SpriteBatch(); // Attach batcher to camera batcher.setProjectionMatrix(cam.combined); shapeRenderer = new ShapeRenderer(); shapeRenderer.setProjectionMatrix(cam.combined); // This is suppose to produce 10 bullets at random places on the background. bullets = new Array<Bullet>(); Bullet bullet = null; float bulletX = 00.0f; float bulletY = 00.0f; for (int i = 0; i < 10; i++) { bulletX = MathUtils.random(-10, 10); bulletY = MathUtils.random(-10, 10); bullet = new Bullet(bulletX, bulletY); AssetLoader.bullet1.flip(true, false); AssetLoader.bullet2.flip(true, false); bullets.add(bullet); } // Call helper methods to initialize instance variables initGameObjects(); initAssets(); } private void initGameObjects() { ball = GameWorld.getBall(); bullet1 = myWorld.getBullet1(); bPop = myWorld.getBulletPop(); scroller = myWorld.getScroller(); } private void initAssets() { bg = AssetLoader.bg; ballAnimation = AssetLoader.ballAnimation; bullet1Animation = AssetLoader.bullet1Animation; ballPopAnimation = AssetLoader.ballPopAnimation; } // This is to take the bullet away when clicked or touched. public void onClick() { for (int i = 0; i < bullets.size; i++) { if (bullets.get(i).getBounds().contains(0, 0)) bullets.removeIndex(i); } } private void drawBackground() { batcher.draw(bg1, background.getX(), background.getY(), background.getWidth(), backgroundMove.getHeight()); } public void render(float runTime) { Gdx.gl.glClearColor(0, 0, 0, 1); Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT); batcher.begin(); // Disable transparency // This is good for performance when drawing images that do not require // transparency. batcher.disableBlending(); drawBackground(); batcher.enableBlending(); // when the bullet hits the ball, it should be disposed or taken away and a ball pop sprite/texture should be put in its place if (bullet1.collides(ball)) { // draws the bPop texture but the bullet does not go just keeps going around, and the bPop texture goes. batcher.draw(AssetLoader.bPop, 195, 273); } batcher.draw(AssetLoader.ballAnimation.getKeyFrame(runTime), ball.getX(), ball.getY(), ball.getWidth(), ball.getHeight()); // this is where i am trying to make the bullets come one by one, and if removed via the onClick() then bPop animation // should play but does not??? if(TimeUtils.nanoTime() - lastShot > shotFreq){ // Create your stuff for (int i = 0; i < bullets.size; i++) { bullets.get(i); batcher.draw(AssetLoader.bullet1Animation.getKeyFrame(runTime), bullet1.getX(), bullet1.getY(), bullet1.getOriginX(), bullet1.getOriginY(), bullet1.getWidth(), bullet1.getHeight(), 1.0f, 1.0f, bullet1.getRotation()); if (bullets.removeValue(bullet1, false)) { batcher.draw(AssetLoader.ballPopAnimation.getKeyFrame(runTime), bPop1.getX(), bPop1.getY(), bPop1.getWidth(), bPop1.getHeight()); } } /* Very important to set the last shot to now, or it will mess up and go full auto */ lastShot = TimeUtils.nanoTime(); } // End SpriteBatch batcher.end(); } } Thank you

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• Extending Expression Blend 4 &amp; Blend for Visual Studio 2012

  - by Chris Skardon

  Just getting this off the bat, I presume this will also work for Blend 5, but I can’t confirm it… Anyhews, I imagine you’re here because you want to know how to create an addin for Blend, so let’s jump right in there! First, and foremost, we’re going to need to ensure our development environment has the right setup, so the checklist: Visual Studio 2012 Blend for Visual Studio 2012 OK, let’s create a new project (class library, .NET 4.5): Hello.Extension The ‘.Extension’ bit is very very important. The addin will not work unless it is named in this way. You can put whatever you want at the front, but it has to have the extension bit. OK, so now we have a solution with one project. To this project we need to add references to the following things: Microsoft.Expression.Extensibility (from c:\program files\Microsoft Visual Studio 11.0\Blend\   -- x86 folder if you are on an x64 windows install) Microsoft.Expression.Framework (same location as above) PresentationCore PresentationFramework WindowsBase System.ComponentModel.Composition Got them? ACE. Let’s now add a project to contain our control, so, create a new WPF Application project, cunningly named something like ‘Hello.Control’… (I’m creating a WPF application here, because I’m too lazy to dig up the correct references, and this will add all the ones I need ) Once that is created, delete the App.xaml and MainWindow.xaml files, we won’t be needing them. You will also need to change the properties of the project itself, so it is only a class library. Once that is done, let’s add a new UserControl, which will be this: <UserControl x:Class="Hello.Control.HelloControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="300"> <Grid> <TextBlock Text="HELLO!!!"/> </Grid> </UserControl> Impressive eh? Now, let’s reference the WPF project from the Extension library. All that’s left now is to code up our extension… So, add a class to the Extension project (name wise doesn’t matter), and make it implement the IPackage interface from the Microsoft.Expression.Extensibility library: public class HelloExtension : IPackage { /**/ } We’ll implement the two methods we need to: public class HelloExtension : IPackage { public void Load(IServices services) { } public void Unload() { } } We’re only really concerned about the Load method in this case, as let’s face it, the extension we have doesn’t need to do a lot to bog off. The interesting thing about the Load method is that it receives an IServices instance. This allows us to get access to all the services that Expression provides, in this case we’re interested in one in particular, the ‘IWindowService’ So, let’s get that bad boy… private IWindowService _windowService; public void Load(IServices services) { _windowService = services.GetService<IWindowService>(); } Nailed it… But why? The WindowService allows us to register our UserControl with Blend, which in turn allows people to activate and see it, which is a big plus point. So, let’s do that… We’ll create an ‘Initialize’ method to create our new control, and add it to the WindowService: private HelloControl _helloControl; public void Initialize() { _helloControl = new HelloControl(); if (_windowService.PaletteRegistry["HelloPanel"] == null) _windowService.RegisterPalette("HelloPanel", _helloControl, "Hello Window"); } First we check that we’re not already registered, and if we’re not we register, the first argument is the identifier used by the service to, well, identify your extension. The second argument is the actual control, the third argument is the name that people will see in the ‘Windows’ menu of Blend itself (so important note here – don’t put anything embarrassing or (need I say it?) sweary…) There are only two things to do now - Call ‘Initialize()’ from our Load method, and Export the class This is easy money – add [Export(typeof(IPackage))] to the top of our class… The full code will (should) look like this: [Export(typeof (IPackage))] public class HelloExtension : IPackage { private HelloControl _helloControl; private IWindowService _windowService; public void Load(IServices services) { _windowService = services.GetService<IWindowService>(); Initialize(); } public void Unload() { } public void Initialize() { _helloControl = new HelloControl(); if (_windowService.PaletteRegistry["HelloControl"] == null) _windowService.RegisterPalette("HelloControl", _helloControl, "Hello Window"); } } If you build this and copy it to your ‘Extensions’ folder in Blend (c:\program files\microsoft visual studio 11.0\blend\) and start Blend, you should see ‘Hello Window’ listed in the Window menu: That as they say is it!

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• Summit reflections

  - by Rob Farley

  So far, my three PASS Summit experiences have been notably different to each other. My first, I wasn’t on the board and I gave two regular sessions and a Lightning Talk in which I told jokes. My second, I was a board advisor, and I delivered a precon, a spotlight and a Lightning Talk in which I sang. My third (last week), I was a full board director, and I didn’t present at all. Let’s not talk about next year. I’m not sure there are many options left. This year, I noticed that a lot more people recognised me and said hello. I guess that’s potentially because of the singing last year, but could also be because board elections can bring a fair bit of attention, and because of the effort I’ve put in through things like 24HOP... Yeah, ok. It’d be the singing. My approach was very different though. I was watching things through different eyes. I looked for the things that seemed to be working and the things that didn’t. I had staff there again, and was curious to know how their things were working out. I knew a lot more about what was going on behind the scenes to make various things happen, and although very little about the Summit was actually my responsibility (based on not having that portfolio), my perspective had moved considerably. Before the Summit started, Board Members had been given notebooks – an idea Tom (who heads up PASS’ marketing) had come up with after being inspired by seeing Bill walk around with a notebook. The plan was to take notes about feedback we got from people. It was a good thing, and the notebook forms a nice pair with the SQLBits one I got a couple of years ago when I last spoke there. I think one of the biggest impacts of this was that during the first keynote, Bill told everyone present about the notebooks. This set a tone of “we’re listening”, and a number of people were definitely keen to tell us things that would cause us to pull out our notebooks. PASSTV was a new thing this year. Justin, the host, featured on the couch and talked a lot of people about a lot of things, including me (he talked to me about a lot of things, I don’t think he talked to a lot people about me). Reaching people through online methods is something which interests me a lot – it has huge potential, and I love the idea of being able to broadcast to people who are unable to attend in person. I’m keen to see how this medium can be developed over time. People who know me will know that I’m a keen advocate of certification – I've been SQL certified since version 6.5, and have even been involved in creating exams. However, I don’t believe in studying for exams. I think training is worthwhile for learning new skills, but the goal should be on learning those skills, not on passing an exam. Exams should be for proving that the skills are there, not a goal in themselves. The PASS Summit is an excellent place to take exams though, and with an attitude of professional development throughout the event, why not? So I did. I wasn’t expecting to take one, but I was persuaded and took the MCM Knowledge Exam. I hadn’t even looked at the syllabus, but tried it anyway. I was very tired, and even fell asleep at one point during it. I’ll find out my result at some point in the future – the Prometric site just says “Tested” at the moment. As I said, it wasn’t something I was expecting to do, but it was good to have something unexpected during the week. Of course it was good to catch up with old friends and make new ones. I feel like every time I’m in the US I see things develop a bit more, with more and more people knowing who I am, who my staff are, and recognising the LobsterPot brand. I missed being a presenter, but I definitely enjoyed seeing many friends on the list of presenters. I won’t try to list them, because there are so many these days that people might feel sad if I don’t mention them. For those that I managed to see, I was pleased to see that the majority of them have lifted their presentation skills since I last saw them, and I happily told them as much. One person who I will mention was Paul White, who travelled from New Zealand to his first PASS Summit. He gave two sessions (a regular session and a half-day), packed large rooms of people, and had everyone buzzing with enthusiasm. I spoke to him after the event, and he told me that his expectations were blown away. Paul isn’t normally a fan of crowds, and the thought of 4000 people would have been scary. But he told me he had no idea that people would welcome him so well, be so friendly and so down to earth. He’s seen the significance of the SQL Server community, and says he’ll be back. It’ll be good to see him there. Will you be there too?

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• OIM 11g - Multi Valued attribute reconciliation of a child form

  - by user604275

  This topic gives a brief description on how we can do reconciliation of a child form attribute which is also multi valued from a flat file . The format of the flat file is (an example): ManagementDomain1|Entitlement1|DIRECTORY SERVER,EMAIL ManagementDomain2|Entitlement2|EMAIL PROVIDER INSTANCE - UMS,EMAIL VERIFICATION In OIM there will be a parent form for fields Management domain and Entitlement.Reconciliation will assign Servers ( which are multi valued) to corresponding Management  Domain and Entitlement .In the flat file , multi valued fields are seperated by comma(,). In the design console, Create a form with 'Server Name' as a field and make it a child form . Open the corresponding Resource Object and add this field for reconcilitaion.While adding , choose 'Multivalued' check box. (please find attached screen shot on how to add it , Child Table.docx) Open process definiton and add child form fields for recociliation. Please click on the 'Create Reconcilitaion Profile' buttton on the resource object tab. The API methods used for child form reconciliation are : 1.           reconEventKey =   reconOpsIntf.createReconciliationEvent(resObjName, reconData,                                                            false); ·                                    ‘False’  here tells that we are creating the recon for a child table . 2.               2.       reconOpsIntf.providingAllMultiAttributeData(reconEventKey, RECON_FIELD_IN_RO, true);                RECON_FIELD_IN_RO is the field that we added in the Resource Object while adding for reconciliation, please refer the screen shot) 3.    reconOpsIntf.addDirectBulkMultiAttributeData(reconEventKey,RECON_FIELD_IN_RO, bulkChildDataMapList);                 bulkChildDataMapList  is coded as below :                 List<Map> bulkChildDataMapList = new ArrayList<Map>();                   for (int i = 0; i < stokens.length; i++) {                            Map<String, String> attributeMap = new HashMap<String, String>();                           String serverName = stokens[i].toUpperCase();                           attributeMap.put("Server Name", stokens[i]);                           bulkChildDataMapList.add(attributeMap);                         } 4                  4.       reconOpsIntf.finishReconciliationEvent(reconEventKey); 5.       reconOpsIntf.processReconciliationEvent(reconEventKey); Now, we have to register the plug-in, import metadata into MDS and then create a scheduled job to execute which will run the reconciliation.

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• Storing non-content data in Orchard

  - by Bertrand Le Roy

  A CMS like Orchard is, by definition, designed to store content. What differentiates content from other kinds of data is rather subtle. The way I would describe it is by saying that if you would put each instance of a kind of data on its own web page, if it would make sense to add comments to it, or tags, or ratings, then it is content and you can store it in Orchard using all the convenient composition options that it offers. Otherwise, it probably isn't and you can store it using somewhat simpler means that I will now describe. In one of the modules I wrote, Vandelay.ThemePicker, there is some configuration data for the module. That data is not content by the definition I gave above. Let's look at how this data is stored and queried. The configuration data in question is a set of records, each of which has a number of properties: public class SettingsRecord { public virtual int Id { get; set;} public virtual string RuleType { get; set; } public virtual string Name { get; set; } public virtual string Criterion { get; set; } public virtual string Theme { get; set; } public virtual int Priority { get; set; } public virtual string Zone { get; set; } public virtual string Position { get; set; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Each property has to be virtual for nHibernate to handle it (it creates derived classed that are instrumented in all kinds of ways). We also have an Id property. The way these records will be stored in the database is described from a migration: public int Create() { SchemaBuilder.CreateTable("SettingsRecord", table => table .Column<int>("Id", column => column.PrimaryKey().Identity()) .Column<string>("RuleType", column => column.NotNull().WithDefault("")) .Column<string>("Name", column => column.NotNull().WithDefault("")) .Column<string>("Criterion", column => column.NotNull().WithDefault("")) .Column<string>("Theme", column => column.NotNull().WithDefault("")) .Column<int>("Priority", column => column.NotNull().WithDefault(10)) .Column<string>("Zone", column => column.NotNull().WithDefault("")) .Column<string>("Position", column => column.NotNull().WithDefault("")) ); return 1; } When we enable the feature, the migration will run, which will create the table in the database. Once we've done that, all we have to do in order to use the data is inject an IRepository<SettingsRecord>, which is what I'm doing from the set of helpers I put under the SettingsService class: private readonly IRepository<SettingsRecord> _repository; private readonly ISignals _signals; private readonly ICacheManager _cacheManager; public SettingsService( IRepository<SettingsRecord> repository, ISignals signals, ICacheManager cacheManager) { _repository = repository; _signals = signals; _cacheManager = cacheManager; } The repository has a Table property, which implements IQueryable<SettingsRecord> (enabling all kind of Linq queries) as well as methods such as Delete and Create. Here's for example how I'm getting all the records in the table: _repository.Table.ToList() And here's how I'm deleting a record: _repository.Delete(_repository.Get(r => r.Id == id)); And here's how I'm creating one: _repository.Create(new SettingsRecord { Name = name, RuleType = ruleType, Criterion = criterion, Theme = theme, Priority = priority, Zone = zone, Position = position }); In summary, you create a record class, a migration, and you're in business and can just manipulate the data through the repository that the framework is exposing. You even get ambient transactions from the work context.

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• The design of a generic data synchronizer, or, an [object] that does [actions] with the aid of [helpers]

  - by acheong87

  I'd like to create a generic data-source "synchronizer," where data-source "types" may include MySQL databases, Google Spreadsheets documents, CSV files, among others. I've been trying to figure out how to structure this in terms of classes and interfaces, keeping in mind (what I've read about) composition vs. inheritance and is-a vs. has-a, but each route I go down seems to violate some principle. For simplicity, assume that all data-sources have a header-row-plus-data-rows format. For example, assume that the first rows of Google Spreadsheets documents and CSV files will have column headers, a.k.a. "fields" (to parallel database fields). Also, eventually, I would like to implement this in PHP, but avoiding language-specific discussion would probably be more productive. Here's an overview of what I've tried. Part 1/4: ISyncable class CMySQL implements ISyncable GetFields() // sql query, pdo statement, whatever AddFields() RemFields() ... _dbh class CGoogleSpreadsheets implements ISyncable GetFields() // zend gdata api AddFields() RemFields() ... _spreadsheetKey _worksheetId class CCsvFile implements ISyncable GetFields() // read from buffer AddFields() RemFields() ... _buffer interface ISyncable GetFields() AddFields($field1, $field2, ...) RemFields($field1, $field2, ...) ... CanAddFields() // maybe the spreadsheet is locked for write, or CanRemFields() // maybe no permission to alter a database table ... AddRow() ModRow() RemRow() ... Open() Close() ... First Question: Does it make sense to use an interface, as above? Part 2/4: CSyncer Next, the thing that does the syncing. class CSyncer __construct(ISyncable $A, ISyncable $B) Push() // sync A to B Pull() // sync B to A Sync() // Push() and Pull() only differ in direction; factor. // Sync()'s job is to make sure that the fields on each side // match, to add fields where appropriate and possible, to // account for different column-orderings, etc., and of // course, to add and remove rows as necessary to sync. ... _A _B Second Question: Does it make sense to define such a class, or am I treading dangerously close to the "Kingdom of Nouns"? Part 3/4: CTranslator? ITranslator? Now, here's where I actually get lost, assuming the above is passable. Sometimes, two ISyncables speak different "dialects." For example, believe it or not, Google Spreadsheets (accessed through the Google Data API "list feed") returns column headers lower-cased and stripped of all spaces and symbols! That is, sys_TIMESTAMP is systimestamp, as far as my code can tell. (Yes, I am aware that the "cell feed" does not strip the name so; however cell-by-cell manipulation is too slow for what I'm doing.) One can imagine other hypothetical examples. Perhaps even the data itself can be in different "dialects." But let's take it as given for now, and not argue this if possible. Third Question: How would you implement "translation"? Note: Taking all this as an exercise, I'm more interested in the "idealized" design, rather than the practical one. (God knows that shipped sailed when I began this project.) Part 4/4: Further Thought Here's my train of thought to demonstrate I've thunk, albeit unfruitfully: First, I thought, primitively, "I'll just modify CMySQL::GetFields() to lower-case and strip field names so they're compatible with Google Spreadsheets." But of course, then my class should really be called, CMySQLForGoogleSpreadsheets, and that can't be right. So, the thing which translates must exist outside of an ISyncable implementor. And surely it can't be right to make each translation a method in CSyncer. If it exists outside of both ISyncable and CSyncer, then what is it? (Is it even an "it"?) Is it an abstract class, i.e. abstract CTranslator? Is it an interface, since a translator only does, not has, i.e. interface ITranslator? Does it even require instantiation? e.g. If it's an ITranslator, then should its translation methods be static? (I learned what "late static binding" meant, today.) And, dear God, whatever it is, how should a CSyncer use it? Does it "have" it? Is it, "it"? Who am I? ...am I, "I"? I've attempted to break up the question into sub-questions, but essentially my question is singular: How does one implement an object A that conceptually "links" (has) two objects b1 and b2 that share a common interface B, where certain pairs of b1 and b2 require a helper, e.g. a translator, to be handled by A? Something tells me that I've overcomplicated this design, or violated a principle much higher up. Thank you all very much for your time and any advice you can provide.

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• How to make creating viewmodels at runtime less painfull

  - by Mr Happy

  I apologize for the long question, it reads a bit as a rant, but I promise it's not! I've summarized my question(s) below In the MVC world, things are straightforward. The Model has state, the View shows the Model, and the Controller does stuff to/with the Model (basically), a controller has no state. To do stuff the Controller has some dependencies on web services, repository, the lot. When you instantiate a controller you care about supplying those dependencies, nothing else. When you execute an action (method on Controller), you use those dependencies to retrieve or update the Model or calling some other domain service. If there's any context, say like some user wants to see the details of a particular item, you pass the Id of that item as parameter to the Action. Nowhere in the Controller is there any reference to any state. So far so good. Enter MVVM. I love WPF, I love data binding. I love frameworks that make data binding to ViewModels even easier (using Caliburn Micro a.t.m.). I feel things are less straightforward in this world though. Let's do the exercise again: the Model has state, the View shows the ViewModel, and the ViewModel does stuff to/with the Model (basically), a ViewModel does have state! (to clarify; maybe it delegates all the properties to one or more Models, but that means it must have a reference to the model one way or another, which is state in itself) To do stuff the ViewModel has some dependencies on web services, repository, the lot. When you instantiate a ViewModel you care about supplying those dependencies, but also the state. And this, ladies and gentlemen, annoys me to no end. Whenever you need to instantiate a ProductDetailsViewModel from the ProductSearchViewModel (from which you called the ProductSearchWebService which in turn returned IEnumerable<ProductDTO>, everybody still with me?), you can do one of these things: call new ProductDetailsViewModel(productDTO, _shoppingCartWebService /* dependcy */);, this is bad, imagine 3 more dependencies, this means the ProductSearchViewModel needs to take on those dependencies as well. Also changing the constructor is painfull. call _myInjectedProductDetailsViewModelFactory.Create().Initialize(productDTO);, the factory is just a Func, they are easily generated by most IoC frameworks. I think this is bad because Init methods are a leaky abstraction. You also can't use the readonly keyword for fields that are set in the Init method. I'm sure there are a few more reasons. call _myInjectedProductDetailsViewModelAbstractFactory.Create(productDTO); So... this is the pattern (abstract factory) that is usually recommended for this type of problem. I though it was genious since it satisfies my craving for static typing, until I actually started using it. The amount of boilerplate code is I think too much (you know, apart from the ridiculous variable names I get use). For each ViewModel that needs runtime parameters you'll get two extra files (factory interface and implementation), and you need to type the non-runtime dependencies like 4 extra times. And each time the dependencies change, you get to change it in the factory as well. It feels like I don't even use an DI container anymore. (I think Castle Windsor has some kind of solution for this [with it's own drawbacks, correct me if I'm wrong]). do something with anonymous types or dictionary. I like my static typing. So, yeah. Mixing state and behavior in this way creates a problem which don't exist at all in MVC. And I feel like there currently isn't a really adequate solution for this problem. Now I'd like to observe some things: People actually use MVVM. So they either don't care about all of the above, or they have some brilliant other solution. I haven't found an indepth example of MVVM with WPF. For example, the NDDD-sample project immensely helped me understand some DDD concepts. I'd really like it if someone could point me in the direction of something similar for MVVM/WPF. Maybe I'm doing MVVM all wrong and I should turn my design upside down. Maybe I shouldn't have this problem at all. Well I know other people have asked the same question so I think I'm not the only one. To summarize Am I correct to conclude that having the ViewModel being an integration point for both state and behavior is the reason for some difficulties with the MVVM pattern as a whole? Is using the abstract factory pattern the only/best way to instantiate a ViewModel in a statically typed way? Is there something like an in depth reference implementation available? Is having a lot of ViewModels with both state/behavior a design smell?

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• Increasing efficiency of N-Body gravity simulation

  - by Postman

  I'm making a space exploration type game, it will have many planets and other objects that will all have realistic gravity. I currently have a system in place that works, but if the number of planets goes above 70, the FPS decreases an practically exponential rates. I'm making it in C# and XNA. My guess is that I should be able to do gravity calculations between 100 objects without this kind of strain, so clearly my method is not as efficient as it should be. I have two files, Gravity.cs and EntityEngine.cs. Gravity manages JUST the gravity calculations, EntityEngine creates an instance of Gravity and runs it, along with other entity related methods. EntityEngine.cs public void Update() { foreach (KeyValuePair<string, Entity> e in Entities) { e.Value.Update(); } gravity.Update(); } (Only relevant piece of code from EntityEngine, self explanatory. When an instance of Gravity is made in entityEngine, it passes itself (this) into it, so that gravity can have access to entityEngine.Entities (a dictionary of all planet objects)) Gravity.cs namespace ExplorationEngine { public class Gravity { private EntityEngine entityEngine; private Vector2 Force; private Vector2 VecForce; private float distance; private float mult; public Gravity(EntityEngine e) { entityEngine = e; } public void Update() { //First loop foreach (KeyValuePair<string, Entity> e in entityEngine.Entities) { //Reset the force vector Force = new Vector2(); //Second loop foreach (KeyValuePair<string, Entity> e2 in entityEngine.Entities) { //Make sure the second value is not the current value from the first loop if (e2.Value != e.Value ) { //Find the distance between the two objects. Because Fg = G * ((M1 * M2) / r^2), using Vector2.Distance() and then squaring it //is pointless and inefficient because distance uses a sqrt, squaring the result simple cancels that sqrt. distance = Vector2.DistanceSquared(e2.Value.Position, e.Value.Position); //This makes sure that two planets do not attract eachother if they are touching, completely unnecessary when I add collision, //For now it just makes it so that the planets are not glitchy, performance is not significantly improved by removing this IF if (Math.Sqrt(distance) > (e.Value.Texture.Width / 2 + e2.Value.Texture.Width / 2)) { //Calculate the magnitude of Fg (I'm using my own gravitational constant (G) for the sake of time (I know it's 1 at the moment, but I've been changing it) mult = 1.0f * ((e.Value.Mass * e2.Value.Mass) / distance); //Calculate the direction of the force, simply subtracting the positions and normalizing works, this fixes diagonal vectors //from having a larger value, and basically makes VecForce a direction. VecForce = e2.Value.Position - e.Value.Position; VecForce.Normalize(); //Add the vector for each planet in the second loop to a force var. Force = Vector2.Add(Force, VecForce * mult); //I have tried Force += VecForce * mult, and have not noticed much of an increase in speed. } } } //Add that force to the first loop's planet's position (later on I'll instead add to acceleration, to account for inertia) e.Value.Position += Force; } } } } I have used various tips (about gravity optimizing, not threading) from THIS question (that I made yesterday). I've made this gravity method (Gravity.Update) as efficient as I know how to make it. This O(N^2) algorithm still seems to be eating up all of my CPU power though. Here is a LINK (google drive, go to File download, keep .Exe with the content folder, you will need XNA Framework 4.0 Redist. if you don't already have it) to the current version of my game. Left click makes a planet, right click removes the last planet. Mouse moves the camera, scroll wheel zooms in and out. Watch the FPS and Planet Count to see what I mean about performance issues past 70 planets. (ALL 70 planets must be moving, I've had 100 stationary planets and only 5 or so moving ones while still having 300 fps, the issue arises when 70+ are moving around) After 70 planets are made, performance tanks exponentially. With < 70 planets, I get 330 fps (I have it capped at 300). At 90 planets, the FPS is about 2, more than that and it sticks around at 0 FPS. Strangely enough, when all planets are stationary, the FPS climbs back up to around 300, but as soon as something moves, it goes right back down to what it was, I have no systems in place to make this happen, it just does. I considered multithreading, but that previous question I asked taught me a thing or two, and I see now that that's not a viable option. I've also thought maybe I could do the calculations on my GPU instead, though I don't think it should be necessary. I also do not know how to do this, it is not a simple concept and I want to avoid it unless someone knows a really noob friendly simple way to do it that will work for an n-body gravity calculation. (I have an NVidia gtx 660) Lastly I've considered using a quadtree type system. (Barnes Hut simulation) I've been told (in the previous question) that this is a good method that is commonly used, and it seems logical and straightforward, however the implementation is way over my head and I haven't found a good tutorial for C# yet that explains it in a way I can understand, or uses code I can eventually figure out. So my question is this: How can I make my gravity method more efficient, allowing me to use more than 100 objects (I can render 1000 planets with constant 300+ FPS without gravity calculations), and if I can't do much to improve performance (including some kind of quadtree system), could I use my GPU to do the calculations?

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