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• CQRS without using others patterns

  - by John Smith

  I would like to explain CQRS to my team of developers. I just can't figure out how to explain it in the simplest way so they can implement the pattern rapidly without any others frameworks. I've read a lot of resources including video and articles but I don't find how to implement CQRS without using others patterns like a service Bus, event sourcing pattern, domain driven design. I know the purpose of these pattern but for the first step, I don't want them to think CQRS and theses patterns must be tied together. My first idea is to say that CQRS is about separating the read part and the write part. The read part is composed only of the UI project, and DAL project. Then the write part is composed of a typical multilayer architecture: UI/BLL/DAL. Then, does CQRS say we must also have two datastore ? What about the notion of commands which reveal the user's intention, is it also something part of CQRS or DDD ? Basically, how to implement CQRS without using others patterns. I concede it's also not that clear in my mind because I've used to work with NCQRS/DDD/Event Sourcing/ServiceBus in my personal project. Thanks

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• What do you think of the following job specification?

  - by m.edmondson

  Just received this out of the blue from a recruiter - a number of things stand out to me: PERSON PROFILE Hard working - with a stay until the job in done mentality Thrive on the pressure of tight weekly development deadlines Good attention to detail to ensure bug free development Ability to test all development work from user's perpective Ability to think like a user as well as a developer Good communication skills to understand new funcationality and bugs Flexibility to contribute outside main responsbilities when needed. BENEFITS Salary dependant on skills Contributary Pension with 4% contribution from employer (after 1 year of service) Private Healthcase (after 1 year of service) 20 days holiday + 3-4 days holiday between Christmas and New year - 1 day extra holiday available each quarter you don't have a day off sick (and an additional day if you are not off sick for the whole year ). Would you want to work here? From what I can see they want a work-a-holic who will crawl out of his death bed in order to not lose holiday entitlement.

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• Multithreded UI desktop application issues

  - by igor

  I am involved into development a rich UI project: desktop windows application. Application uses asynchronous invocations and in its turn it should be ready to process external messages (events). The problem is clear: at first time it was built as a simple prototype and it was not stress tested and all was fine. Then application was grown: the number of calls to server and number of events from server are high and performance is low. What is more users noticed that sometimes performance is extremal low. Asynchronous invocations based on thread pool (BeginInvoke, EndInvoke), external events are going from WCF service (.NET 3.5). My goal is synchronization of all tasks and putting priorities to every executions in desktop application. My question is: is there any practice how to reach my goal: patterns, task priority list, others? What should I do at first, second and next times? Thanks

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• Java - learning / migrating fast

  - by Yippie-Kai-Yay

  This is not one of those questions like "How do I learn Java extremely fast, I know nothing about programming, but I heard Java is cool, yo". I have an interview for a Java Software Developer in a couple of weeks and the thing is that I think that I know C++ really good and I am somewhat good at C# (like, here I can probably answer on a lot of questions related to these languages), but I have almost zero experience with Java. I have a lot of projects written in both languages, I participiated in several open-source projects (mostly C++, though). Now, what should I do (in your opinion) to prepare myself for this Java interview. I guess migrating from C# to Java should be kind of fast, especially when you know a lot about programming in global, patterns, modern techniques and have a lot of practical experience behind you. But still two weeks is obviously not enough to get Java in-depth - so what should I focus on to have the best chances to pass the interview? Thank you.

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• Why are exceptions considered better than explicit error testing?

  - by Richard Keller

  I often come across heated blog posts where the author uses the argument of "exceptions vs explicit error checking" to advocate their preferred language over some other language. The general consensus seems to be that languages which make use of exceptions are inherently better / cleaner than languages which rely heavily on error checking through explicit function calls. Is the use of exceptions considered better programming practice than explicit error checking, and if so, why?

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• Backend devs put down by user stories

  - by Szili

  I planned to slice in backend development into to the user stories vertically. But a backend guy on our team started to complain that this makes their work invisible. My answer was that at the sprint planning and review meetings we discuss backend tasks in front of stakeholders so it makes it visible, and maintaining a high quality during the project will result a slower startin pace than other teams, but we will have a stable velocity during the project. And velocity is highly visible to stakeholders. He still insist having stories like: "As a developer I need to have a domain layer so I can encapsulate business logic." How can I solve the issue before it pollutes the team? The root of the issue is that our management systematically consider backend work as invisible and call backed devs miners, or other pejorative terms.

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• Help with complex MVVM (multiple views)

  - by jsjslim

  I need help creating view models for the following scenario: Deep, hierarchical data Multiple views for the same set of data Each view is a single, dynamically-changing view, based on the active selection Depending on the value of a property, display different types of tabs in a tab control My questions: Should I create a view-model representation for each view (VM1, VM2, etc)? 1. Yes: a. Should I model the entire hierarchical relationship? (ie, SubVM1, HouseVM1, RoomVM1) b. How do I keep all hierarchies in sync? (e.g, adding/removing nodes) 2. No: a. Do I use a huge, single view model that caters for all views? Here's an example of a single view Figure 1: Multiple views updated based on active room. Notice Tab control Figure 2: Different active room. Multiple views updated. Tab control items changed based on object's property. Figure 3: Different selection type. Entire view changes

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• Am I experienced enough to learn and develop immediately using Ruby on Rails?

  - by acheong87

  General Question I understand that discussions revolving around questions of this form run the risk of becoming too specific to help others. So, perhaps a better, general question would be: What kind of experience, if any, translates easily to Ruby on Rails; and if none, then what's the learning curve like, in comparison to other popular languages? Background I have the opportunity to build a website using whatever technologies I wish to use. It's a fairly simple website, for listing products, taking payments, managing customer data, providing a back-end portal for employees to manage data, possibly hooking in flight information (the products are travel related), possibly integrating a blog and all the social-networking goodies. Specific Problem I have to let the client know by tonight whether I'm interested in taking up this project, before he talks to other potential developers, but I'm on the fence. I already work a full-time C++ development job, so the money doesn't do it for me. It's the opportunity to (be paid to) learn some new technologies and to have a real, running product in the end. I've heard and read great things about Ruby, and am really intrigued. I zipped through some introductory Ruby tutorials, no sweat. However I found the Rails tutorials a little overwhelming, especially not being able to try it out anywhere. And researching Rails hosts like Heroku and EngineYard makes me think that maybe I don't know what I'm getting myself into. The ship's leaving port! I wish I had more time to learn, better yet play with the language, but I have to decide soon! Should I venture or pass? Additional Details My experiences are in C/C++/Tcl/Perl/PHP/jQuery, and basic knowledge of Java/C#. I didn't study C.S. formally so I wasn't exposed to design principles, programming paradigms, etc., which is my greatest concern. Will my lack of understanding in this realm make RoR frustrating to learn? Will it be so incompatible with a C++ "way" of thinking that I'll wish I never started? Am I putting my client at risk by attempting this? If it helps, I'm quick to learn new things (self-taught so far) and care a great deal about correctness, using things for their intended purposes, and so on. I've read numerous recommendations of Agile Development with Rails and would love to read it (though perhaps, while developing in parallel, for shortness of time). Worse comes to worst, I'd give up and do the standard LAMP gig, of course, not charging the client for wasted time. But I'm hoping to avoid the project altogether if it's gonna come down to that! Thanks in advance for any tips, insights, votes of confidence, votes of discouragement (for the better), and such.

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• Consistency of an object

  - by Stefano Borini

  I tend to keep my objects consistent during their lifetime. In some cases, setting up an object requires multiple calls to different routines. For example, a connection object may operate in this way: Connection c = new Connection(); c.setHost("http://whatever") c.setPort(8080) c.connect() please note this is just a stupid example to let you understand the point. In between calls to setHost and setPort the object is inconsistent, because the Port has not been specified yet, so this code would crash Connection c = new Connection(); c.setHost("http://whatever") c.connect() Meaning that it's a requisite for connect() to have previous calls to both setHost and setPort, otherwise it won't be able to operate as its state is inconsistent. You may fix the issue with a default value, but there may be cases where no sensible default may be devised. We assume in the later example that there's no default for the port, and therefore a call to c.connect() without first calling both setHost and setPort will be an inconsistent state of the object. This, to me, points at an incorrect interface design, but I may be wrong, so I want to hear your opinion. Do you organize your interface so that the object is always in a consistent (i.e. workable) state both before and after the call ? Edit: Please don't try to solve the problem I gave above. I know how to solve that. My question is much broader in sense. I am looking for a design principle, officially or informally stated, regarding consistency of object state between calls.

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• How to design a scalable notification system?

  - by Trent

  I need to write a notification system manager. Here is my requirements: I need to be able to send a Notification on different platforms, which may be totally different (for exemple, I need to be able to send either an SMS or an E-mail). Sometimes the notification may be the same for all recipients for a given platform, but sometimes it may be a notification per recipients (or several) per platform. Each notification can contain platform specific payload (for exemple an MMS can contains a sound or an image). The system need to be scalable, I need to be able to send a very large amount of notification without crashing either the application or the server. It is a two step process, first a customer may type a message and choose a platform to send to, and the notification(s) should be created to be processed either real-time either later. Then the system needs to send the notification to the platform provider. For now, I end up with some though but I don't know how scalable it will be or if it is a good design. I've though of the following objects (in a pseudo language): a generic Notification object: class Notification { String $message; Payload $payload; Collection<Recipient> $recipients; } The problem with the following objects is what if I've 1.000.000 recipients ? Even if the Recipient object is very small, it'll take too much memory. I could also create one Notification per recipient, but some platform providers requires me to send it in batch, meaning I need to define one Notification with several Recipients. Each created notification could be stored in a persistent storage like a DB or Redis. Would it be a good it to aggregate this later to make sure it is scalable? On the second step, I need to process this notification. But how could I distinguish the notification to the right platform provider? Should I use an object like MMSNotification extending an abstract Notification? or something like Notification.setType('MMS')? To allow to process a lot of notification at the same time, I think a messaging queue system like RabbitMQ may be the right tool. Is it? It would allow me to queue a lot of notification and have several worker to pop notification and process them. But what if I need to batch the recipients as seen above? Then I imagine a NotificationProcessor object for which I could I add NotificationHandler each NotificationHandler would be in charge to connect the platform provider and perform notification. I can also use an EventManager to allow pluggable behavior. Any feedbacks or ideas? Thanks for giving your time. Note: I'm used to work in PHP and it is likely the language of my choice.

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• Teaching programming to a non-CS graduate

  - by Shahzada

  I have a couple of friends interested in computer programming, but they're non-CS graduates; some of them have very little experience in software testing field (some of them took some basic software testing courses). I am going to be working with them on teaching basic computer programming, and computer science fundamentals (data structures etc). My questions are; What language should I start with? What are essential computer science topics that I should cover before jumping them into computer programming? What readings can I incorporate to make the topic interesting and non-overwhelming? If we want to spend a year on it, what topics should take priority and must be covered in 12 months? Again, these are non computer science folks, and I want to keep the learning as much fun as possible. Thanks everyone.

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• Automated deployment/installation of development tools

  - by thegreendroid

  My team is looking to automate installation/deployment of all of our development tools. The main driver for this is to ensure that everyone in the team has a consistent development environment setup and to also allow a new recruit to get up and running easily. By development environment I mean tools like SCM, toolchains, IDEs etc. and by consistent I mean everyone using the same version of compiler to build code (this is very important!). Here are a few of our requirements – Allow unattended (silent) install of our entire dev setup by running a single script Ability to deploy selective updates (new versions) for specific tools Ability to report which tools are installed and their specific version numbers Must work on Windows (Linux would be a bonus) Must be easy to maintain What are some of the tools that you've used to automate such a task?

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• How can a large company foster excellence in its engineers?

  - by Joshiatto

  I am tasked with improving the skills (quality & speed) of engineers in my company. Here are some ideas: Pair Programming TDD Automated Check-in Policies Talks given by experts Awards for coding excellence Encourage competition among engineers to contribute to GitHub Publish standards and practices docs on the intranet site "Gamification" of engineering. Somehow make becoming badasses into a game they will enjoy playing Training Showcase github checkins on screens around the office Add an "engineer of the month" to the intranet home page How can I drive traffic to the intranet home page? What crazy futuristic idea would drive engineers to go to the page every day to see who of their peers are making more money than them (inferred via recognition) and then go off and improve their skills and productivity to see their standings improve on the home page??? Or any ideas just to foster collaboration and love for their jobs so they start taking more pride in their work?? Don't take my ideas as symptomatic of our org. I take full responsibility for not knowing the right way to do this.

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• How important is positive feedback in code reviews?

  - by c_maker

  Is it important to point out the good parts of the code during a code review and the reasons why it is good? Positive feedback might be just as useful for the developer being reviewed and for the others that participate in the review. We are doing reviews using an online tool, so developers can open reviews for their committed code and others can review their code within a given time period (e.g. 1 week). Others can comment on the code or other reviewer's comments. Should there be a balance between positive and negative feedback?

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• Is there a procedural graphical programming environment?

  - by Marc

  I am searching for a graphical programming environment for procedural programming in which you can integrate some or all of the common sources of calculation procedures, such as Excel sheets, MATLAB scripts or even .NET assemblies. I think of something like a flowchart configurator in which you define the procedures via drag& drop using flow-statements (if-else, loops, etc.). Do you know of any systems heading in this direction?

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• Need recommendation for transferring ASP.NET MVC skills to PHP

  - by Tuck

  I am looking to translate my skills in .NET to PHP - specifically in regards to ASP.NET MVC. At work I am currently using .NET MVC 2.0 on a variety of projects and thoroughly enjoy the platform. Specifically I enjoy the very minimal configuration required to get a project up and running (just create the project, define routes, and start coding), as well as the ability for controller actions to return different items (i.e. ActionResult, JsonResult). Another piece I really like is the way the view/model interaction can be handled. For example I like being able to call return View(model) and having a view page (.aspx) load and having the full model object available to the view, regardless of the model type. I'm looking for a PHP implementation of MVC that is the most similiar to what I am already familiar with. I don't anything apart from the MVC functionality. I've looked at Zend, Symfony, CodeIgniter, etc. and, while they look like they'll be fun to play with in the future, they provide much more functionality than I need. I'd prefer to write my own DAL, form helpers, delegate handlers, authentication/ACL pieces, etc. In short, I just need something to handle the routing and view interactions and will worry about the model implementation myself. Can someone please point me to some lightweight code that accomplishes or comes close to accomplishing my objectives above. Or, can someone identify just the portions of a larger framework that do the same (again, I'm not currently interested in implementing something on a big framework, just the MVC portion and want to implement the model portion myself as much as possible). Thanks in advance.

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• Is there a clean separation of my layers with this attempt at Domain Driven Design in XAML and C#

  - by Buddy James

  I'm working on an application. I'm using a mixture of TDD and DDD. I'm working hard to separate the layers of my application and that is where my question comes in. My solution is laid out as follows Solution MyApp.Domain (WinRT class library) Entity (Folder) Interfaces(Folder) IPost.cs (Interface) BlogPosts.cs(Implementation of IPost) Service (Folder) Interfaces(Folder) IDataService.cs (Interface) BlogDataService.cs (Implementation of IDataService) MyApp.Presentation(Windows 8 XAML + C# application) ViewModels(Folder) BlogViewModel.cs App.xaml MainPage.xaml (Contains a property of BlogViewModel MyApp.Tests (WinRT Unit testing project used for my TDD) So I'm planning to use my ViewModel with the XAML UI I'm writing a test and define my interfaces in my system and I have the following code thus far. [TestMethod] public void Get_Zero_Blog_Posts_From_Presentation_Layer_Returns_Empty_Collection() { IBlogViewModel viewModel = _container.Resolve<IBlogViewModel>(); viewModel.LoadBlogPosts(0); Assert.AreEqual(0, viewModel.BlogPosts.Count, "There should be 0 blog posts."); } viewModel.BlogPosts is an ObservableCollection<IPost> Now.. my first thought is that I'd like the LoadBlogPosts method on the ViewModel to call a static method on the BlogPost entity. My problem is I feel like I need to inject the IDataService into the Entity object so that it promotes loose coupling. Here are the two options that I'm struggling with: Not use a static method and use a member method on the BlogPost entity. Have the BlogPost take an IDataService in the constructor and use dependency injection to resolve the BlogPost instance and the IDataService implementation. Don't use the entity to call the IDataService. Put the IDataService in the constructor of the ViewModel and use my container to resolve the IDataService when the viewmodel is instantiated. So with option one the layers will look like this ViewModel(Presentation layer) - Entity (Domain layer) - IDataService (Service Layer) or ViewModel(Presentation layer) - IDataService (Service Layer)

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• Record management system java web framework

  - by Kamil Tomšík

  We're currently reconsidering technologies and frameworks to get more agile with "simple" RMS CRUD-based projects. In short, short-living things like this Right now we have a custom extension on top of SmartGWT but after some time it has proven not to be flexible enough. I also personally dislike the java-js compilation process and the whole GWT codebase. Not only is the design ugly, it also makes certain low-level js things very complicated if not completely impossible. So what I'm looking for is: closest to web as possible, like JSF or possibly Tapestry, it is very important to be able get "low" and weave framework if necessary. Happens more often than we thought. datagrid capable - Ext.js & PrimeFaces looks pretty good, Vaadin does too. db-schema generators (optional, no matter in which way) If it were only on me, I'd probably stick to Ext.js + custom rest-based java solution, possibly generated from database schema (not sure about concrete tooling yet). I only have experience with vanilla Ext.js, vanilla GWT and JSF 2.0 / Seam, so it hard for me to judge or even propose other frameworks. What would be your proposition? What are the problems you've faced? What was your solution and how hard do you think it was to deal with them in "big picture"?

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• Binary on the Coat of Arms of the Governor General of Canada

  - by user132636

  Can you help me further this investigation? Here is about 10% of the work I have done on it. I present it only to see if there are any truly curious people among you. I made a video a few weeks ago showing some strange things about the Governor General's Coat of Arms and the binary on it. Today, I noticed something kinda cool and thought I would share. Here is the binary as it appears on the COA: 110010111001001010100100111010011 As DEC: 6830770643 (this is easily found on the web) Take a close look at that number. What do you notice about it? It has a few interesting features, but here is the one no one has pointed out... Split it down the middle and you have 68307 70643. The first digit is double the value of the last digit. The second digit is double the second last digit. The third digit is half of the third to last digit. And the middle ones are even or neutral. At first, I thought of it as energy. ++-nnnn+-- But actually you can create something else with it using the values. 221000211. See how that works. You may be asking why that is significant. Bare with me. I know 99% are rolling their eyes. 221000211 as base3 gives you this as binary: 100011101000111 100011101000111 as HEX is 4747, which converts to "GG". Initials of Governor General. GG.ca is his website. When you convert to base 33 (there are 33 digits in the original code) you get "GOV" Interesting? :D There is a lot more to it. I'll continue to show some strange coincidences if anyone is interested. Sorry if I am not explaining this correctly. By now you have probably figured out that I have no background in this. Which is why I am here. Thank you.

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• Best Design Pattern for Coupling User Interface Components and Data Structures

  - by szahn

  I have a windows desktop application with a tree view. Due to lack of a sound data-binding solution for a tree view, I've implemented my own layer of abstraction on it to bind nodes to my own data structure. The requirements are as follows: Populate a tree view with nodes that resemble fields in a data structure. When a node is clicked, display the appropriate control to modify the value of that property in the instance of the data structure. The tree view is populated with instances of custom TreeNode classes that inherit from TreeNode. The responsibility of each custom TreeNode class is to (1) format the node text to represent the name and value of the associated field in my data structure, (2) return the control used to modify the property value, (3) get the value of the field in the control (3) set the field's value from the control. My custom TreeNode implementation has a property called "Control" which retrieves the proper custom control in the form of the base control. The control instance is stored in the custom node and instantiated upon first retrieval. So each, custom node has an associated custom control which extends a base abstract control class. Example TreeNode implementation: //The Tree Node Base Class public abstract class TreeViewNodeBase : TreeNode { public abstract CustomControlBase Control { get; } public TreeViewNodeBase(ExtractionField field) { UpdateControl(field); } public virtual void UpdateControl(ExtractionField field) { Control.UpdateControl(field); UpdateCaption(FormatValueForCaption()); } public virtual void SaveChanges(ExtractionField field) { Control.SaveChanges(field); UpdateCaption(FormatValueForCaption()); } public virtual string FormatValueForCaption() { return Control.FormatValueForCaption(); } public virtual void UpdateCaption(string newValue) { this.Text = Caption; this.LongText = newValue; } } //The tree node implementation class public class ExtractionTypeNode : TreeViewNodeBase { private CustomDropDownControl control; public override CustomControlBase Control { get { if (control == null) { control = new CustomDropDownControl(); control.label1.Text = Caption; control.comboBox1.Items.Clear(); control.comboBox1.Items.AddRange( Enum.GetNames( typeof(ExtractionField.ExtractionType))); } return control; } } public ExtractionTypeNode(ExtractionField field) : base(field) { } } //The custom control base class public abstract class CustomControlBase : UserControl { public abstract void UpdateControl(ExtractionField field); public abstract void SaveChanges(ExtractionField field); public abstract string FormatValueForCaption(); } //The custom control generic implementation (view) public partial class CustomDropDownControl : CustomControlBase { public CustomDropDownControl() { InitializeComponent(); } public override void UpdateControl(ExtractionField field) { //Nothing to do here } public override void SaveChanges(ExtractionField field) { //Nothing to do here } public override string FormatValueForCaption() { //Nothing to do here return string.Empty; } } //The custom control specific implementation public class FieldExtractionTypeControl : CustomDropDownControl { public override void UpdateControl(ExtractionField field) { comboBox1.SelectedIndex = comboBox1.FindStringExact(field.Extraction.ToString()); } public override void SaveChanges(ExtractionField field) { field.Extraction = (ExtractionField.ExtractionType) Enum.Parse(typeof(ExtractionField.ExtractionType), comboBox1.SelectedItem.ToString()); } public override string FormatValueForCaption() { return string.Empty; } The problem is that I have "generic" controls which inherit from CustomControlBase. These are just "views" with no logic. Then I have specific controls that inherit from the generic controls. I don't have any functions or business logic in the generic controls because the specific controls should govern how data is associated with the data structure. What is the best design pattern for this?

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• Implement service layer in MVC

  - by Dan H

  We have a defined service layer hosted in WCF. We are now building a website that will need to use the services functionality. The website is being written in ASP.NET MVC 4 and I'm trying to decide how to reference the WCF service from the MVC app. It's a large complex website and it will be changing on a weekly basis. My first reaction is to abstract out the service references (About 7 services on this one WCF host) and create a service ref facade library with which the website interacts. But, I don't know exactly how to use the service facade in MVC. I'm starting to think the Models will be responsible for it because when the controller gets a model, that model should call the service (if needed) and return what the controller asked. I'm trying to avoid having the MVC app know details of the service references. So, I could have a model factory that creates whatever model the controllers need and they can use the service facade to accomplish it. Is this a good plan, or am I off track?

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• I'm an experienced PHP programmer, how would it be for me to learn and use Django and Ruby on Rails?

  - by João Paulo Apolinário Passos

  I'm an experienced PHP programmer, I still have lots to learn but I consider myself experienced. I sometimes use pure PHP and sometimes some framework like CodeIgniter. I always wanted to learn new technologies like Python and Ruby, and their best frameworks for web are Django and Ruby on Rails, but I want to ask to persons like me who migrated from PHP to some of this technologies if is it worth it; Thank you

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• Integrating application ad-support - best practice

  - by Jarede

  Considering the review that came out in March: Researchers from Purdue University in collaboration with Microsoft claim that third-party advertising in free smartphone apps can be responsible for as much as 65 percent to 75 percent of an app's energy consumption. Is there a best practice for integrating advert support into mobile applications, so as to not drain user battery too much. When you fire up Angry Birds on your Android phone, the researchers found that the core gaming component only consumes about 18 percent of total app energy. The biggest battery suck comes from the software powering third-party ads and analytics accounting for 45 percent of total app energy, according to the study. Has anyone invoked better ways of keeping away from the "3G Tail", as the report puts it. Is it better/possible to download a large set of adverts that are cached for a few hours, and using them to populate your ad space, to avoid constant use of the wifi/3g radios. Are there any best practices for the inclusion of adverts in mobile apps?

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• What design patterns are the worst or most narrowly defined?

  - by Akku

  For every programming project, Managers with past programming experience try to shine when they recommend some design patterns for your project. I like design patterns when they make sense or if you need a scalbale solution. I've used Proxies, Observers and Command patterns in a positive way for example, and do so every day. But I'm really hesitant to use say a Factory pattern if there's only one way to create an object, as a factory might make it all easier in the future, but complicates the code and is pure overhead. So, my question is in respect to my future career and my answer to manager types throwing random pattern-names around: Which design patterns did you use, that threw you back overall? Which are the worst design patterns, that you shouldn't have a look at if it's not that only single situation where it makes sense (read: which design patterns are very narrowly defined)? (It's like I was looking for the negative reviews of an overall good product of amazon to see what bugged people most in using design patterns). And I'm not talking about Anti-Patterns here, but about Patterns that are usually thought of as "good" patterns. Edit: As some answered, the problem is most often that patterns are not "bad" but "used wrong". If you know patterns, that are often misused or even difficult to use, they would also fit as an answer.

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• How accurate is "Business logic should be in a service, not in a model"?

  - by Jeroen Vannevel

  Situation Earlier this evening I gave an answer to a question on StackOverflow. The question: Editing of an existing object should be done in repository layer or in service? For example if I have a User that has debt. I want to change his debt. Should I do it in UserRepository or in service for example BuyingService by getting an object, editing it and saving it ? My answer: You should leave the responsibility of mutating an object to that same object and use the repository to retrieve this object. Example situation: class User { private int debt; // debt in cents private string name; // getters public void makePayment(int cents){ debt -= cents; } } class UserRepository { public User GetUserByName(string name){ // Get appropriate user from database } } A comment I received: Business logic should really be in a service. Not in a model. What does the internet say? So, this got me searching since I've never really (consciously) used a service layer. I started reading up on the Service Layer pattern and the Unit Of Work pattern but so far I can't say I'm convinced a service layer has to be used. Take for example this article by Martin Fowler on the anti-pattern of an Anemic Domain Model: There are objects, many named after the nouns in the domain space, and these objects are connected with the rich relationships and structure that true domain models have. The catch comes when you look at the behavior, and you realize that there is hardly any behavior on these objects, making them little more than bags of getters and setters. Indeed often these models come with design rules that say that you are not to put any domain logic in the the domain objects. Instead there are a set of service objects which capture all the domain logic. These services live on top of the domain model and use the domain model for data. (...) The logic that should be in a domain object is domain logic - validations, calculations, business rules - whatever you like to call it. To me, this seemed exactly what the situation was about: I advocated the manipulation of an object's data by introducing methods inside that class that do just that. However I realize that this should be a given either way, and it probably has more to do with how these methods are invoked (using a repository). I also had the feeling that in that article (see below), a Service Layer is more considered as a façade that delegates work to the underlying model, than an actual work-intensive layer. Application Layer [his name for Service Layer]: Defines the jobs the software is supposed to do and directs the expressive domain objects to work out problems. The tasks this layer is responsible for are meaningful to the business or necessary for interaction with the application layers of other systems. This layer is kept thin. It does not contain business rules or knowledge, but only coordinates tasks and delegates work to collaborations of domain objects in the next layer down. It does not have state reflecting the business situation, but it can have state that reflects the progress of a task for the user or the program. Which is reinforced here: Service interfaces. Services expose a service interface to which all inbound messages are sent. You can think of a service interface as a façade that exposes the business logic implemented in the application (typically, logic in the business layer) to potential consumers. And here: The service layer should be devoid of any application or business logic and should focus primarily on a few concerns. It should wrap Business Layer calls, translate your Domain in a common language that your clients can understand, and handle the communication medium between server and requesting client. This is a serious contrast to other resources that talk about the Service Layer: The service layer should consist of classes with methods that are units of work with actions that belong in the same transaction. Or the second answer to a question I've already linked: At some point, your application will want some business logic. Also, you might want to validate the input to make sure that there isn't something evil or nonperforming being requested. This logic belongs in your service layer. "Solution"? Following the guidelines in this answer, I came up with the following approach that uses a Service Layer: class UserController : Controller { private UserService _userService; public UserController(UserService userService){ _userService = userService; } public ActionResult MakeHimPay(string username, int amount) { _userService.MakeHimPay(username, amount); return RedirectToAction("ShowUserOverview"); } public ActionResult ShowUserOverview() { return View(); } } class UserService { private IUserRepository _userRepository; public UserService(IUserRepository userRepository) { _userRepository = userRepository; } public void MakeHimPay(username, amount) { _userRepository.GetUserByName(username).makePayment(amount); } } class UserRepository { public User GetUserByName(string name){ // Get appropriate user from database } } class User { private int debt; // debt in cents private string name; // getters public void makePayment(int cents){ debt -= cents; } } Conclusion All together not much has changed here: code from the controller has moved to the service layer (which is a good thing, so there is an upside to this approach). However this doesn't look like it had anything to do with my original answer. I realize design patterns are guidelines, not rules set in stone to be implemented whenever possible. Yet I have not found a definitive explanation of the service layer and how it should be regarded. Is it a means to simply extract logic from the controller and put it inside a service instead? Is it supposed to form a contract between the controller and the domain? Should there be a layer between the domain and the service layer? And, last but not least: following the original comment Business logic should really be in a service. Not in a model. Is this correct? How would I introduce my business logic in a service instead of the model?

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