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• Integer Surrogate Key?

  - by CitadelCSAlum

  I need something real simple, that for some reason I am unable to accomplish to this point. I have also been unable to Google the answer surprisingly. I need to number the entries in different tables uniquely. I am aware of AUTO INCREMENT in MySQL and that it will be involved. My situation would be as follows If I had a table like Table EXAMPLE ID - INTEGER FIRST_NAME - VARCHAR(45) LAST_NAME - VARCHAR(45) PHONE - VARCHAR(45) CITY - VARCHAR(45) STATE - VARCHAR(45) ZIP - VARCHAR(45) This would be the setup for the table where ID is an integer that is auto-incremented every time an entry is inserted into the table. The thing I need is that I do not want to have to account for this field when inserting data into the database. From my understanding this would be a surrogate key, that I can tell the database to automatically increment and I do not have to include it in the INSERT STATEMENT so instead of INSERT INTO EXAMPLE VALUES (2,'JOHN','SMITH',333-333-3333,'NORTH POLE'.... I can leave out the first ID column and just write something like INSERT INTO EXAMPLE VALUES ('JOHN','SMITH'.....etc) Notice I Wouldnt have to define the ID column... I know this is a very common task to do, but for some reason I cant get to the bottom of it. I am using MySQL, just to clarify. Thanks alot

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• Create dynamic factory method in PHP (< 5.3)

  - by fireeyedboy

  How would one typically create a dynamic factory method in PHP? By dynamic factory method, I mean a factory method that will autodiscover what objects there are to create, based on some aspect of the given argument. Preferably without registering them first with the factory either. I'm OK with having the possible objects be placed in one common place (a directory) though. I want to avoid your typical switch statement in the factory method, such as this: public static function factory( $someObject ) { $className = get_class( $someObject ); switch( $className ) { case 'Foo': return new FooRelatedObject(); break; case 'Bar': return new BarRelatedObject(); break; // etc... } } My specific case deals with the factory creating a voting repository based on the item to vote for. The items all implement a Voteable interface. Something like this: Default_User implements Voteable ... Default_Comment implements Voteable ... Default_Event implements Voteable ... Default_VoteRepositoryFactory { public static function factory( Voteable $item ) { // autodiscover what type of repository this item needs // for instance, Default_User needs a Default_VoteRepository_User // etc... return new Default_VoteRepository_OfSomeType(); } } I want to be able to drop in new Voteable items and Vote repositories for these items, without touching the implementation of the factory.

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• Webbased data modelling and management tool

  - by pixeldude

  Is there a web-based tool available, where I am able to... ...define data models (like in a database admin tool) ...fill in data (in custom web forms, not too generic) with basic features like completion ...import data from CSV oder Excel Sheets ...export data to CSV or SQL ...create snapshots of my data models (versions, diff, etc.) ...share my data models ...discuss/collaborate with other people about my data models Well, I can develop something like this in PHP or with Ruby or whatever. But this is such a common task, where the application support could be a lot better. And it would be language and database independent. This would help to maintain data models in different versions and you can maybe share your data models with others, extend it with your team members, etc. There is a website called FreeBase, which allows you to define a data entity model and fill in data, which also has export features, but I need to define my own data model with my own granularity and structure. And it should not be shared in public if I don't want to. How do you solve problems like this yourself?

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• algorithm || method to write prog

  - by fatai

  I am one of the computer science student. My wonder is everyone solve problem with different or same method, but actually I dont know whether they use method or I dont know whether there are such common method to approach problem. All teacher give us problem which in simple form sometimes, but they dont introduce any approach or method(s) so that we can first choose method then apply that one to problem , afterward find solution then write code. I have found one method when I failed the course, More accurately, When I counter problem in language , I will get more paper and then ; first, input/ output step ; my prog will take this / these there argument(s) and return namely X , ex : in c, input length is not known and at same type , so I must use pointer desired output is in form of package , so use structure second, execution part ; in that step , I am writing all step which are goes to final output ex : in python ; 1.) [ + , [- , 4 , [ * , 1 , 2 ]], 5] 2.) [ + , [- , 4 , 2 ],5 ] 3.) [ + , 2 , 5] 4.) 7 ==> return 7 third, I will write test code ex : in c++ input : append 3 4 5 6 vector_x remove 0 1 desired output vector_x holds : 5 6 But now, I wonder other method ; used to construct class :::: for c++ , python, java used to communicate classes / computers used for solving embedded system problem ::::: for c Why I wonder , because I learn if you dont costruct algorithm on paper, you may achieve your goal. Like no money no lunch , I can say no algorithm no prog therefore , feel free when you write your own method , a way which is introduced by someone else but you are using and you find it is so efficient

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• Rendering LaTeX on third-party websites?

  - by A. Rex

  There are some sites on the web that render LaTeX into some more readable form, such as Wikipedia, some Wordpress blogs, and MathOverflow. They may use images, MathML, jsMath, or something like that. There are other sites on the web where LaTeX appears inline and is not rendered, such as the arXiv, various math forums, or my email. In fact, it is quite common to see an arXiv paper's abstract with raw LaTeX in it, e.g. this paper. Is there a plugin available for Firefox, or would it be possible to write one, that renders LaTeX within pages that do not provide a rendering mechanism themselves? (The LaTeX would be enclosed within dollar signs, e.g. $\pi$. See the arXiv link above.) Some notes: It may be impossible to render some of the code, because authors often copy-paste code directly from their source TeX files, which may contain things like "\cite{foo}" or undefined commands. These should be left alone. This question is a repost of a question from MathOverflow that was closed for not being related to math. There is one answer there, which is helpful, but perhaps Stack Overflow can provide better answers. I program a lot, but Javascript is not my specialty, so comments along the lines of "look at this library" are not particularly helpful to me (but may be to others).

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• Business Objects - Containers or functional?

  - by Walter

  Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object. Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)? One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object. The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about how to save a customer if I'm consuming the object? Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense? EDIT These results are very similar to our debates. One vote to one side or another completely changes the direction. Does anyone else want to add their 2 cents? EDIT Eventhough the answer sampling is small, it appears that the majority believe that functionality in a business object is acceptable as long as it is simple but persistence is best placed in a separate class/layer. We'll give this a try. Thanks for everyone's input...

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• Design suggestion for expression tree evaluation with time-series data

  - by Lirik

  I have a (C#) genetic program that uses financial time-series data and it's currently working but I want to re-design the architecture to be more robust. My main goals are: sequentially present the time-series data to the expression trees. allow expression trees to access previous data rows when needed. to optimize performance of the data access while evaluating the expression trees. keep a common interface so various types of data can be used. Here are the possible approaches I've thought about: I can evaluate the expression tree by passing in a data row into the root node and let each child node use the same data row. I can evaluate the expression tree by passing in the data row index and letting each node get the data row from a shared DataSet (currently I'm passing the row index and going to multiple synchronized arrays to get the data). Hybrid: an immutable data set is accessible by all of the expression trees and each expression tree is evaluated by passing in a data row. The benefit of the first approach is that the data row is being passed into the expression tree and there is no further query done on the data set (which should increase performance in a multithreaded environment). The drawback is that the expression tree does not have access to the rest of the data (in case some of the functions need to do calculations using previous data rows). The benefit of the second approach is that the expression trees can access any data up to the latest data row, but unless I specify what that row is, I'll have to iterate through the rows and figure out which one is the last one. The benefit of the hybrid is that it should generally perform better and still provide access to the earlier data. It supports two basic "views" of data: the latest row and the previous rows. Do you guys know of any design patterns or do you have any tips that can help me build this type of system? Should I use a DataSet to hold and present the data, or are there more efficient ways to present rows of data while maintaining a simple interface? FYI: All of my code is written in C#.

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• "Priming" a whole database in MSSQL for first-hit speed

  - by David Spillett

  For a particular apps I have a set of queries that I run each time the database has been restarted for any reason (server reboot usually). These "prime" SQL Server's page cache with the common core working set of the data so that the app is not unusually slow the first time a user logs in afterwards. One instance of the app is running on an over-specced arrangement where the SQL box has more RAM than the size of the database (4Gb in the machine, the DB is under 1.5Gb currently and unlikely to grow too much relative to that in the near future). Is there a neat/easy way of telling SQL Server to go away and load everything into RAM? It could be done the hard way by having a script scan sysobjects & sysindexes and running SELECT * FROM <table> WITH(INDEX(<index_name>)) ORDER BY <index_fields> for every key and index found, which should cause every used page to be read at least once and so be in RAM, but is there a cleaner or more efficient way? All planned instances where the database server is stopped are out-of-normal-working-hours (all the users are at most one timezone away and unlike me none of them work at silly hours) so such a process (until complete) slowing down users more than the working set not being primed at all would is not an issue.

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• ASP.NET RadioButton messing with the name (groupname)

  - by Hojou

  I got a templated control (a repeater) listing some text and other markup. Each item has a radiobutton associated with it, making it possible for the user to select ONE of the items created by the repeater. The repeater writes the radiobutton setting its id and name generated with the default asp.net naming convention making each radiobutton a full 'group'. This means all radiobuttons are independant on each other, which again unfortunately means i can select all radiobuttons at the same time. The radiobutton has the clever attribute 'groupname' used to set a common name so they get grouped together and thus should be dependant (so i can only select one at a time). The problem is - this doesn't work - the repeater makes sure the id and thus the name (which controls the grouping) are different. Since i use a repeater (could have been a listview or any other templated databound control) i can't use the RadioButtonList. So where does that leave me? I know i've had this problem before and solved it. I know almost every asp.net programmer must have had it too, so why can't i google and find a solid solution to the problem? I came across solutions to enforce the grouping by javascript (ugly!) or even to handle the radiobuttons as non-server controls, forcing me to do a Request.Form[name] to read the status. I also tried experimenting with overriding the name attribute on the PreRender event - unfortunately the owning page and masterpage again overrides this name to reflect the full id/name so i end up with the same wrong result. If you have no better solution than i posted, you are still very welcome to post your thoughts - atleast i'll know that my friend 'jack' is right about how messed up 'asp.net' is sometimes ;)

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• nServiceBus - No all commands being received by handler

  - by SimonB

  In a test project based of the nServiceBus pub/sub sample, I've replace the bus.publish with bus.send in the server. The server sends 50 messages with a 1sec wait after each 5 (ie 10 burst of 5 messages). The client does not get all the messages. The soln has 3 projects - Server, Client, and common messages. The server and client are hosted via the nServiceBus generic host. Only a single bus is defined. Both client and server are configured to use StructureMap builder and BinarySerialisation. Server Endpoint: public class EndPointConfig : AsA_Publisher, IConfigureThisEndpoint, IWantCustomInitialization { public void Init() { NServiceBus.Configure.With() .StructureMapBuilder() .BinarySerializer(); } } Server Code : for (var nextId = 1; nextId <= 50; nextId++) { Console.WriteLine("Sending {0}", nextId); IDataMsg msg = new DataMsg { Id = nextId, Body = string.Format("Batch Msg #{0}", nextId) }; _bus.SendLocal(msg); Console.WriteLine(" ...sent {0}", nextId); if ((nextId % 5) == 0) Thread.Sleep(1000); } Client Endpoint: public class EndPointConfig : AsA_Client, IConfigureThisEndpoint, IWantCustomInitialization { public void Init() { NServiceBus.Configure.With() .StructureMapBuilder() .BinarySerializer(); } } Client Clode: public class DataMsgHandler : IMessageHandler<IDataMsg> { public void Handle(IDataMsg msg) { Console.WriteLine("DataMsgHandler.Handle({0}, {1}) - ({2})", msg.Id, msg.Body, Thread.CurrentThread.ManagedThreadId); } } Client and Server App.Config: <MsmqTransportConfig InputQueue="nsbt02a" ErrorQueue="error" NumberOfWorkerThreads="1" MaxRetries="5" /> <UnicastBusConfig DistributorControlAddress="" DistributorDataAddress=""> <MessageEndpointMappings> <add Messages="Test02.Messages" Endpoint="nsbt02a" /> </MessageEndpointMappings> </UnicastBusConfig> All run via VisualStudio 2008. All 50 messages are sent - but after the 1st or 2nd batch. only 1 msg per batch is sent? Any ideas? I'm assuming config or misuse but ....?

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• How to properly force a Blackberry Java application to install using Loader.exe

  - by Kevin White

  I want to include the Application Loader process in a software installation, to ensure that users get our software installed on their Blackberry by the time our installer software finishes. I know this is possible, because Aerize Card Loader (http://aerize.com/blackberry/software/loader/) does this. When you install their software, if your Blackberry is connected the Application Loader will come up and force the .COD file to install to the device. I can't make it work. Looking at RIM's own documentation, I need to: Place the ALX and COD files into a subfolder here: C:\Program Files\Common Files\Research In Motion\Shared\Applications\ Add a path to the ALX file in HKCU\Software\Research In Motion\Blackberry\Loader\Packages Index the application, by executing this at the command line: loader.exe /index Start the force load, by doing this: loader.exe /defaultUSB /forceload When I execute that last command, the Application Loader comes up and says that all applications are up to date and nothing needs to be done. If I execute loader.exe by double-clicking on it (or typing in the command with no parameters), I get the regular Application Loader wizard. It shows my program as listed, but un-checked. If I check it and click next, it will install to the Blackberry. (This is the part that I want to avoid, and that Aerize Card Loader's install process avoids.) What am I missing? It appears that the Aerize installer is doing something different but I haven't been able to ascertain what.

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• What is the best software design to use in this scenario

  - by domdefelice

  I need to generate HTML snippets using jQuery. The creation of those snippets depends on some data. The data is stored server-side, in session (where PHP is used). At the moment I achieved this - retrieving the data from the server via AJAX in form of JSON - and building the snippets via specific javascript functions that read those data The problem is that the complexity of the data is getting bigger and hence the serialization into JSON is getting even more difficult since I can't do it automatically. I can't do it automatically because some information are sensible so I generate a "stripped" version to send to the client. I know it is difficult to understand without any code to read, but I am hoping this is a common scenario and would be glad for any tip, suggestion or even design-pattern you can give me. Should I store both a complete and a stripped data on the server and then use some library to automatically generate the JSON from the stripped data? But this also means I have to get the two data synchronized. Or maybe I could move the logic server-side, this way avoiding sending the data. But this means sending javascript code (since I rely on jQuery). Maybe not a good idea. Feel free to ask me more details if this is not clear. Thank you for any help

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• Data Mappers, Models and Images

  - by James

  Hi, I've seen and read plenty of blog posts and forum topics talking about and giving examples of Data Mapper / Model implementations in PHP, but I've not seen any that also deal with saving files/images. I'm currently working on a Zend Framework based project and I'm doing some image manipulation in the model (which is being passed a file path), and then I'm leaving it to the mapper to save that file to the appropriate location - is this common practise? But then, how do you deal with creating say 3 different size images from the one passed in? At the moment I have a "setImage($path_to_tmp_name)" which checks the image type, resizes and then saves back to the original filename. A call to "getImagePath()" then returns the current file path which the data mapper can use and then change with a call to "setImagePath($path)" once it's saved it to the appropriate location, say "/content/my_images". Does this sound practical to you? Also, how would you deal with getting the URL to that image? Do you see that as being something that the model should be providing? It seems to me like that model should worry about where the images are being stored or ultimately how they're accessed through a browser and so I'm inclined to put that in the ini file and just pass the URL prefix to the view through the controller. Does that sound reasonable? I'm using GD for image manipulation - not that that's of any relevance. UPDATE: I've been wondering if the image resizing should be done in the model at all. The model could require that it's provided a "main" image and a "thumb" image, both of certain dimensions. I've thought about creating a "getImageSpecs()" function in the model that would return something that defines the required sizes, then a separate image manipulation class could carry out the resizing and (perhaps in the controller?) and just pass the final paths in to the model using something like "setImagePaths($images)". Any thoughts much appreciated :) James.

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• New to web development - backend questions

  - by James

  I'm new to web development although I'm confident in the roadmap for the front-end. I need direction on two things: Basic architecture Back-end technologies For architecture, what do I need to get started? From what I know, its: Get a domain name registered (godaddy?) Find a web host ??? anything else? or start developing the site? I don't think its that easy, there must be something I'm missing, right? For the back-end technologies, I have application development experience with Java and Python, but how likely is it to find a back-end hosting site that supports these languages over PHP? Is PHP a better choice? If I stick with what I know for the back-end, am I sabotaging myself later on? If I need help, how is the market for a python/java developer vs. a php developer? What do I need to know about databases? I have some basic SQL experience. Do hosting sites have limitations on the type of databases or bandwidth I need to worry about? I'm working through some of the common sites: StackOverflow, Sitepoint forums, Google, etc...are there other resources I should use?

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• Help to resolve 'Out of memory' exception when calling DrawImage

  - by Jack Juiceson

  Hi guys, About one percent of our users experience sudden crash while using our application. The logs show below exception, the only thing in common that I've seen so far is that, they all have XP SP3. Thanks in advance Out of memory. at System.Drawing.Graphics.CheckErrorStatus(Int32 status) at System.Drawing.Graphics.DrawImage(Image image, Rectangle destRect, Int32 srcX, Int32 srcY, Int32 srcWidth, Int32 srcHeight, GraphicsUnit srcUnit, ImageAttributes imageAttrs, DrawImageAbort callback, IntPtr callbackData) at System.Drawing.Graphics.DrawImage(Image image, Rectangle destRect, Int32 srcX, Int32 srcY, Int32 srcWidth, Int32 srcHeight, GraphicsUnit srcUnit, ImageAttributes imageAttr, DrawImageAbort callback) at System.Drawing.Graphics.DrawImage(Image image, Rectangle destRect, Int32 srcX, Int32 srcY, Int32 srcWidth, Int32 srcHeight, GraphicsUnit srcUnit, ImageAttributes imageAttr) at System.Windows.Forms.ControlPaint.DrawBackgroundImage(Graphics g, Image backgroundImage, Color backColor, ImageLayout backgroundImageLayout, Rectangle bounds, Rectangle clipRect, Point scrollOffset, RightToLeft rightToLeft) at System.Windows.Forms.Control.PaintBackground(PaintEventArgs e, Rectangle rectangle, Color backColor, Point scrollOffset) at System.Windows.Forms.Control.PaintBackground(PaintEventArgs e, Rectangle rectangle) at System.Windows.Forms.Control.OnPaintBackground(PaintEventArgs pevent) at System.Windows.Forms.ScrollableControl.OnPaintBackground(PaintEventArgs e) at System.Windows.Forms.Control.PaintTransparentBackground(PaintEventArgs e, Rectangle rectangle, Region transparentRegion) at System.Windows.Forms.Control.PaintBackground(PaintEventArgs e, Rectangle rectangle, Color backColor, Point scrollOffset) at System.Windows.Forms.Control.PaintBackground(PaintEventArgs e, Rectangle rectangle) at System.Windows.Forms.Control.OnPaintBackground(PaintEventArgs pevent) at System.Windows.Forms.ScrollableControl.OnPaintBackground(PaintEventArgs e) at System.Windows.Forms.Control.PaintTransparentBackground(PaintEventArgs e, Rectangle rectangle, Region transparentRegion) at System.Windows.Forms.Control.PaintBackground(PaintEventArgs e, Rectangle rectangle, Color backColor, Point scrollOffset) at System.Windows.Forms.Control.PaintBackground(PaintEventArgs e, Rectangle rectangle) at System.Windows.Forms.Control.OnPaintBackground(PaintEventArgs pevent) at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs) at System.Windows.Forms.Control.WmPaint(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) Operation System Information ---------------------------- Name = Windows XP Edition = Home Service Pack = Service Pack 3 Version = 5.1.2600.196608 Bits = 32

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• maven-release-plugin: Perform fails with 'working directory "...workspace\target\checkout\workspace"

  - by Ed

  Hi, I have maven project that fails when release:perform is called, though release;prepare works as expected. I have found the bug report (below) which certainly seems to resemble the issue I have but not entirely sure I understand the problem: MRELEASE516 The last few lines of output I get: [INFO] Executing: cmd.exe /X /C "p4 -d E:\hudson\jobs\myHudsonJob\workspace\target\checkout -p 10.20.0.38:1666 client -d myProjectWorkspace-MavenSCM-E:\hudson\jobs\myHudsonJob\workspace\target\checkout" [INFO] Executing goals 'deploy'... [WARNING] Base directory is a file. Using base directory as POM location. [WARNING] Maven will be executed in interactive mode, but no input stream has been configured for this MavenInvoker instance. [INFO] ------------------------------------------------------------------------ [ERROR] BUILD ERROR [INFO] ------------------------------------------------------------------------ [INFO] Error executing Maven. Working directory "E:\hudson\jobs\myHudsonJob\workspace\target\checkout\workspace" does not exist! From reading the bug report the possible cause of the error is related to my modules' structure, I've tried to outline it below: /workspace | |+ pom.xml (root pom whose parent is the build pom, | calling release:perform on this pom) | [Modules: moduleA and moduleB] | |- moduleA |+ pom.xml (parent is also build pom) |+ build/pom.xml (the build pom - no custom parent) |- moduleB |+ pom.xml (parent is build pom) It seems that the root pom should be in some common directory inside 'workspace' from the error but tried that and doesn't work, nor make sense as to why I need it. What does the warning Base directory is a file want me to do instead?! It then figures that the base directory is workspace which then means the working directory is not found...any ideas? Thanks in advance.

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• database schema eligible for delta synchronization

  - by WilliamLou

  it's a question for discussion only. Right now, I need to re-design a mysql database table. Basically, this table contains all the contract records I synchronized from another database. The contract record can be modified, deleted or users can add new contract records via GUI interface. At this stage, the table structure is exactly the same as the Contract info (column: serial number, expiry date etc.). In that case, I can only synchronize the whole table (delete all old records, replace with new ones). If I want to delta(only synchronize with modified, new, deleted records) synchronize the table, how should I change the database schema? here is the method I come up with, but I need your suggestions because I think it's a common scenario in database applications. 1)introduce a sequence number concept/column: for each sequence, mark the new added records, modified records, deleted records with this sequence number. By recording the last synchronized sequence number, only pass those records with higher sequence number; 2) because deleted contracts can be added back, and the original table has primary key constraints, should I create another table for those deleted records? or add a flag column to indicate if this contract has been deleted? I hope I explain my question clearly. Anyway, if you know any articles or your own suggestions about this, please let me know. Thanks!

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• Test Views in ASP.NET MVC2 (ala RSpec)

  - by Dmitriy Nagirnyak

  Hi, I am really missing heavily the ability to test Views independently of controllers. The way RSpec does it. What I want to do is to perform assertions on the rendered view (where no controller is involved!). In order to do so I should provide required Model, ViewData and maybe some details from HttpContextBase (when will we get rid of HttpContext!). So far I have not found anything that allows doing it. Also it might heavily depend on the ViewEngine being used. List of things that views might contain are: Partial views (may be nested deeply). Master pages (or similar in other view engines). Html helpers generating links and other elements. Generally almost anything in a range of common sense :) . Also please note that I am not talking about client-side testing and thus Selenium is just not related to it at all. It is just plain .NET testing. So are there any options to actually do the testing of views? Thanks, Dmitriy.

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• Parsing basic math equations for children's educational software?

  - by Simucal

  Inspired by a recent TED talk, I want to write a small piece of educational software. The researcher created little miniature computers in the shape of blocks called "Siftables". [David Merril, inventor - with Siftables in the background.] There were many applications he used the blocks in but my favorite was when each block was a number or basic operation symbol. You could then re-arrange the blocks of numbers or operation symbols in a line, and it would display an answer on another siftable block. So, I've decided I wanted to implemented a software version of "Math Siftables" on a limited scale as my final project for a CS course I'm taking. What is the generally accepted way for parsing and interpreting a string of math expressions, and if they are valid, perform the operation? Is this a case where I should implement a full parser/lexer? I would imagine interpreting basic math expressions would be a semi-common problem in computer science so I'm looking for the right way to approach this. For example, if my Math Siftable blocks where arranged like: [1] [+] [2] This would be a valid sequence and I would perform the necessary operation to arrive at "3". However, if the child were to drag several operation blocks together such as: [2] [\] [\] [5] It would obviously be invalid. Ultimately, I want to be able to parse and interpret any number of chains of operations with the blocks that the user can drag together. Can anyone explain to me or point me to resources for parsing basic math expressions? I'd prefer as much of a language agnostic answer as possible.

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• Any HTTP proxies with explicit, configurable support for request/response buffering and delayed conn

  - by Carlos Carrasco

  When dealing with mobile clients it is very common to have multisecond delays during the transmission of HTTP requests. If you are serving pages or services out of a prefork Apache the child processes will be tied up for seconds serving a single mobile client, even if your app server logic is done in 5ms. I am looking for a HTTP server, balancer or proxy server that supports the following: A request arrives to the proxy. The proxy starts buffering in RAM or in disk the request, including headers and POST/PUT bodies. The proxy DOES NOT open a connection to the backend server. This is probably the most important part. The proxy server stops buffering the request when: A size limit has been reached (say, 4KB), or The request has been received completely, headers and body Only now, with (part of) the request in memory, a connection is opened to the backend and the request is relayed. The backend sends back the response. Again the proxy server starts buffering it immediately (up to a more generous size, say 64KB.) Since the proxy has a big enough buffer the backend response is stored completely in the proxy server in a matter of miliseconds, and the backend process/thread is free to process more requests. The backend connection is immediately closed. The proxy sends back the response to the mobile client, as fast or as slow as it is capable of, without having a connection to the backend tying up resources. I am fairly sure you can do 4-6 with Squid, and nginx appears to support 1-3 (and looks like fairly unique in this respect). My question is: is there any proxy server that empathizes these buffering and not-opening-connections-until-ready capabilities? Maybe there is just a bit of Apache config-fu that makes this buffering behaviour trivial? Any of them that it is not a dinosaur like Squid and that supports a lean single-process, asynchronous, event-based execution model? (Siderant: I would be using nginx but it doesn't support chunked POST bodies, making it useless for serving stuff to mobile clients. Yes cheap 50$ handsets love chunked POSTs... sigh)

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• Free tools/libraries to compare tables with filtering in different databases and visualize/sync diff

  - by MicMit

  I am building certain GUI in C# for a content manager and looking for the tools or code snippets or open libraries ( code ideally in C# ) which allow me the following : 1. For table A in database X (test ) and table A in database Y (production) and for a simple filter ( e.g. listname = "XYZ" ) I need to show additions/deletions/updates in some way. which might be side-by-side or just html report 2 record added html table with some fields 2 record deleted html table with some fields Considering that this task is very common, I guess, certain components should exist ? Components either return some collections from parameters given for further visualizing or just produce reports mentioned above. 2. I need to push changes for the filter I mentioned in 1 and update table in production database for this filter only ( ie for the particular list approved by content person). Again probably there are certain SQL code generators - components in addition to diffs or standalone. 3. The key thing tools/libraries - should be suitable for integration with the existing application in C#.

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• "Pattern matching" of algebraic type data constructors

  - by jetxee

  Let's consider a data type with many constructors: data T = Alpha Int | Beta Int | Gamma Int Int | Delta Int I want to write a function to check if two values are produced with the same constructor: sameK (Alpha _) (Alpha _) = True sameK (Beta _) (Beta _) = True sameK (Gamma _ _) (Gamma _ _) = True sameK _ _ = False Maintaining sameK is not much fun, it is potentially buggy. For example, when new constructors are added to T, it's easy to forget to update sameK. I omitted one line to give an example: -- it’s easy to forget: -- sameK (Delta _) (Delta _) = True The question is how to avoid boilerplate in sameK? Or how to make sure it checks for all T constructors? The workaround I found is to use separate data types for each of the constructors, deriving Data.Typeable, and declaring a common type class, but I don't like this solution, because it is much less readable and otherwise just a simple algebraic type works for me: {-# LANGUAGE DeriveDataTypeable #-} import Data.Typeable class Tlike t where value :: t -> t value = id data Alpha = Alpha Int deriving Typeable data Beta = Beta Int deriving Typeable data Gamma = Gamma Int Int deriving Typeable data Delta = Delta Int deriving Typeable instance Tlike Alpha instance Tlike Beta instance Tlike Gamma instance Tlike Delta sameK :: (Tlike t, Typeable t, Tlike t', Typeable t') => t -> t' -> Bool sameK a b = typeOf a == typeOf b

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• deepcopy and python - tips to avoid using it?

  - by blackkettle

  Hi, I have a very simple python routine that involves cycling through a list of roughly 20,000 latitude,longitude coordinates and calculating the distance of each point to a reference point. def compute_nearest_points( lat, lon, nPoints=5 ): """Find the nearest N points, given the input coordinates.""" points = session.query(PointIndex).all() oldNearest = [] newNearest = [] for n in xrange(nPoints): oldNearest.append(PointDistance(None,None,None,99999.0,99999.0)) newNearest.append(obj2) #This is almost certainly an inappropriate use of deepcopy # but how SHOULD I be doing this?!?! for point in points: distance = compute_spherical_law_of_cosines( lat, lon, point.avg_lat, point.avg_lon ) k = 0 for p in oldNearest: if distance < p.distance: newNearest[k] = PointDistance( point.point, point.kana, point.english, point.avg_lat, point.avg_lon, distance=distance ) break else: newNearest[k] = deepcopy(oldNearest[k]) k += 1 for j in range(k,nPoints-1): newNearest[j+1] = deepcopy(oldNearest[j]) oldNearest = deepcopy(newNearest) #We're done, now print the result for point in oldNearest: print point.station, point.english, point.distance return I initially wrote this in C, using the exact same approach, and it works fine there, and is basically instantaneous for nPoints<=100. So I decided to port it to python because I wanted to use SqlAlchemy to do some other stuff. I first ported it without the deepcopy statements that now pepper the method, and this caused the results to be 'odd', or partially incorrect, because some of the points were just getting copied as references(I guess? I think?) -- but it was still pretty nearly as fast as the C version. Now with the deepcopy calls added, the routine does it's job correctly, but it has incurred an extreme performance penalty, and now takes several seconds to do the same job. This seems like a pretty common job, but I'm clearly not doing it the pythonic way. How should I be doing this so that I still get the correct results but don't have to include deepcopy everywhere?

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• What is the general feeling about reflection extensions in std::type_info?

  - by Evan Teran

  I've noticed that reflection is one feature that developers from other languages find very lacking in c++. For certain applications I can really see why! It is so much easier to write things like an IDE's auto-complete if you had reflection. And certainly serialization APIs would be a world easier if we had it. On the other side, one of the main tenets of c++ is don't pay for what you don't use. Which makes complete sense. That's something I love about c++. But it occurred to me there could be a compromise. Why don't compilers add extensions to the std::type_info structure? There would be no runtime overhead. The binary could end up being larger, but this could be a simple compiler switch to enable/disable and to be honest, if you are really concerned about the space savings, you'll likely disable exceptions and RTTI anyway. Some people cite issues with templates, but the compiler happily generates std::type_info structures for template types already. I can imagine a g++ switch like -fenable-typeinfo-reflection which could become very popular (and mainstream libs like boost/Qt/etc could easily have a check to generate code which uses it if there, in which case the end user would benefit with no more cost than flipping a switch). I don't find this unreasonable since large portable libraries like this already depend on compiler extensions. So why isn't this more common? I imagine that I'm missing something, what are the technical issues with this?

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• Silverlight and WCF Ria Services

  - by Flex_Addicted

  Hi guys, I've created a new Silverlight 3 Business Application with VS 2008. The creation has completed correctly. When I try to open the xaml, it opens but in meanwhile this error is shown: Failed to load metadata assembly System.Windows.Controls.Data.Input.Design, Version=2.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35. Exception message: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.. Stack Trace: at System.Reflection.Module._GetTypesInternal(StackCrawlMark& stackMark) at System.Reflection.Assembly.GetTypes() at MS.Internal.Package.MetadataLoader.RegisterDesignTimeMetadata(Assembly assembly, LogCallback logger)An exception of type ArgumentNullException was caught when calling IRegisterMetadata on type System.Windows.Controls.Data.Input.VisualStudio.Design.MetadataRegistration. Exception Message: Value cannot be null. Parameter name: type. Stack Trace: at Microsoft.Windows.Design.Metadata.AttributeTableBuilder.AddCallback(Type type, AttributeCallback callback) at System.Windows.Controls.Data.Input.VisualStudio.Design.MetadataRegistration.AddAttributes(AttributeTableBuilder builder) at System.Windows.Controls.Design.Common.MetadataRegistrationBase.BuildAttributeTable() at System.Windows.Controls.Data.Input.VisualStudio.Design.MetadataRegistration.Register() at MS.Internal.Package.MetadataLoader.RegisterDesignTimeMetadata(Assembly assembly, LogCallback logger)Failed to load metadata assembly System.Windows.Controls.Design, Version=2.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35. Exception message: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.. Stack Trace: at System.Reflection.Module._GetTypesInternal(StackCrawlMark& stackMark) at System.Reflection.Assembly.GetTypes() at MS.Internal.Package.MetadataLoader.RegisterDesignTimeMetadata(Assembly assembly, LogCallback logger)Failed to load metadata assembly System.Windows.Controls.Navigation.Design, Version=2.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35. Exception message: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.. Stack Trace: at System.Reflection.Module._GetTypesInternal(StackCrawlMark& stackMark) at System.Reflection.Assembly.GetTypes() at MS.Internal.Package.MetadataLoader.RegisterDesignTimeMetadata(Assembly assembly, LogCallback logger) Why? Any solutions? Thank you in advance.

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