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  • Best Practise for Writing a POS System

    - by Gary
    Hi, I'm putting together a basic POS system in C# that needs to print to a receipt printer and open a cash drawer. Do I have to use the Microsoft Point of Service SDK? I've been playing around with printing to my Samsung printer using the Windows driver that came with it, and it seems to work great. I assume though that other printers may not come with Windows drivers and then I would be stuck? Or would I be able to simply use the Generic/Text Driver to print to any printer that supports it? For the cash drawer I would need to send codes directly to the COM port which is fine with me, if it saves me the hassle of helping clients setup OPOS drivers on there systems. Am I going down the wrong path here? Thanks, Gary

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  • singleton vs factory?

    - by fayer
    i've got 3 Log classes that all implements iLog interface: DatabaseLog FileLog ScreenLog there can only be one instance of them. initially i though of using single pattern for each class but then i thought why not use a factory for instantiation instead, cause then i wont have to create single pattern for each one of them and for all future Log classes. and maybe someone would want them as multiple objects in the future. so my questions is: should i use factory or singleton pattern here?

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  • Which pattern should be used for editing properties with modal view controller on iPhone?

    - by Matthew Daugherty
    I am looking for a good pattern for performing basic property editing via a modal view on the iPhone. Assume I am putting together an application that works like the Contacts application. The "detail" view controller displays all of the contact's properties in a UITableView. When the UITableView goes into edit mode a disclosure icon is displayed in the cells. Clicking a cell causes a modal "editor" view controller to display a view that allows the user to modify the selected property. This view will often contain only a single text box or picker. The user clicks Cancel/Save and the "editor" view is dismissed and the "detail" view is updated. In this scenario, which view is responsible for updating the model? The "editor" view could update the property directly using Key-Value Coding. This appears in the CoreDataBooks example. This makes sense to me on some level because it treats the property as the model for the editor view controller. However, this is not the pattern suggested by the View Controller Programming Guide. It suggests that the "editor" view controller should define a protocol that the "detail" controller adopts. When the user indicates they are done with the edit, the "detail" view controller is called back with the entered value and it dismisses the "editor" view. Using this approach the "detail" controller updates the model. This approach seems problematic if you are using the same "editor" view for multiple properties since there is only a single call-back method. Would love to get some feedback on what approach works best.

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  • Repository pattern with lazying loading using POCO

    - by Simon G
    Hi, I'm in the process of starting a new project and creating the business objects and data access etc. I'm just using plain old clr objects rather than any orms. I've created two class libraries: 1) Business Objects - holds all my business objects, all this objects are light weight with only properties and business rules. 2) Repository - this is for all my data access. The majority of my objects will have child list in and my question is what is the best way to lazy load these values as I don't want to bring back unnecessary information if I dont need to. I've thought about when using the "get" on the child property to check if its "null" and if it is call my repository to get the child information. This has two problems from what I can see: 1) The object "knows" how to get itself I would rather no data access logic be held in the object. 2) This required both classes to reference each other which in visual studio throws a circular dependency error. Does anyone have any suggestions on how to overcome this issue or any recommendations on my projects layout and where it can be improved? Thanks

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  • How can I effectively test a scripting engine?

    - by ChaosPandion
    I have been working on an ECMAScript implementation and I am currently working on polishing up the project. As a part of this, I have been writing tests like the following: [TestMethod] public void ArrayReduceTest() { var engine = new Engine(); var request = new ExecScriptRequest(@" var a = [1, 2, 3, 4, 5]; a.reduce(function(p, c, i, o) { return p + c; }); "); var response = (ExecScriptResponse)engine.PostWithReply(request); Assert.AreEqual((double)response.Data, 15D); } The problem is that there are so many points of failure in this test and similar tests that it almost doesn't seem worth it. It almost seems like my effort would be better spent reducing coupling between modules. To write a true unit test I would have to assume something like this: [TestMethod] public void CommentTest() { const string toParse = "/*First Line\r\nSecond Line*/"; var analyzer = new LexicalAnalyzer(toParse); { Assert.IsInstanceOfType(analyzer.Next(), typeof(MultiLineComment)); Assert.AreEqual(analyzer.Current.Value, "First Line\r\nSecond Line"); } } Doing this would require me to write thousands of tests which once again does not seem worth it.

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  • Async Load JavaScript Files with Callback

    - by Gcoop
    Hi All, I am trying to write an ultra simple solution to load a bunch of JS files asynchronously. I have the following script below so far. However the callback is sometimes called when the scripts aren't actually loaded which causes a variable not found error. If I refresh the page sometimes it just works because I guess the files are coming straight from the cache and thus are there quicker than the callback is called, it's very strange? var Loader = function () { } Loader.prototype = { require: function (scripts, callback) { this.loadCount = 0; this.totalRequired = scripts.length; this.callback = callback; for (var i = 0; i < scripts.length; i++) { this.writeScript(scripts[i]); } }, loaded: function (evt) { this.loadCount++; if (this.loadCount == this.totalRequired && typeof this.callback == 'function') this.callback.call(); }, writeScript: function (src) { var self = this; var s = document.createElement('script'); s.type = "text/javascript"; s.async = true; s.src = src; s.addEventListener('load', function (e) { self.loaded(e); }, false); var head = document.getElementsByTagName('head')[0]; head.appendChild(s); } } Is there anyway to test that a JS file is completely loaded, without putting something in the actual JS file it's self, because I would like to use the same pattern to load libraries out of my control (GMaps etc). Invoking code, just before the tag. var l = new Loader(); l.require([ "ext2.js", "ext1.js"], function() { var config = new MSW.Config(); Refraction.Application().run(MSW.ViewMapper, config); console.log('All Scripts Loaded'); }); Thanks for any help.

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  • Fix common library functions, or abandon then?

    - by Ian Boyd
    Imagine i have a function with a bug in it: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" return City+", "+State; } So the call: MakeLocation("Springfield", "MO"); would return "Springfield, MO" Now there's a slight problem, what if the user called: MakeLocation("Springfield, MO", "OH"); The called it wrong, obviously. But the function would return "Springfield, MO, OH". The system was functioning like this for many years, until i noticed the function being used wrong, and i corrected it. And i also updated the original function to catch such an obvious mistake - in case it's happening elsewhere: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" if (City.Contains, ",") throw new EMakeLocationException("City name contains a comma. You probably didn't mean that"); return City+", "+State; } And testing showed the problem fixed. Except we missed an edge case, and the customer found it. So now the moral dillema. Do you ever add new sanity checks, safety checks, assertions to exising code? Or do you call the old function abandoned, and have a new one: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" return City+", "+State; } Boolean MakeLocation2(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" if (City.Contains, ",") throw new EMakeLocationException("City name contains a comma. You probably didn't mean that"); return City+", "+State; } The same can apply for anything: Question FetchQuestion(Int id) { if (id == 0) throw new EFetchQuestionException("No question ID specified"); ... } Do you risk breaking existing code, at the expense of existing code being wrong?

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  • Etiquette for refactoring other people's sourcecode?

    - by Prutswonder
    Our team of software developers consists of a bunch of experienced programmers with a variety of programming styles and preferences. We do not have standards for everything, just the bare necessities to prevent total chaos. Recently, I bumped into some refactoring done by a colleague. My code looked somewhat like this: public Person CreateNewPerson(string firstName, string lastName) { var person = new Person() { FirstName = firstName, LastName = lastName }; return person; } Which was refactored to this: public Person CreateNewPerson (string firstName, string lastName) { Person person = new Person (); person.FirstName = firstName; person.LastName = lastName; return person; } Just because my colleague needed to update some other method in one of the classes I wrote, he also "refactored" the method above. For the record, he's one of those developers that despises syntactic sugar and uses a different bracket placement/identation scheme than the rest of us. My question is: What is the (C#) programmer's etiquette for refactoring other people's sourcecode (both semantic and syntactic)?

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  • Notification between J2EE components.

    - by Pratik
    Hi There! I have a design problem . My application has multiple J2EE components ,In simple terms one acts as a service provider(Non UI) and others are consumers(UI webapp) . The consumer gets the configuration data from the service provider(this basically reads the data from DB) during the start up and stores it in the Cache. The cache gets refreshed after periodic time to reflect any changes done at the database. The Problem Apart from the cache refresh ,I also want to notify the consumers when someone changes the DB . that configuration has been changed please reload it. What notification mechanism's can I use to achieve this. Thanks! Pratik

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  • Recommend .NET data access layer/middle tier

    - by Simon G
    Hi, I'm currently creating an MVC application that will likely to expand to include a silverlight, wpf and possible windows phone all using the same data. So I've created a class library to keep all my objects in and I've created the MVC app. My question is what would be the best way to access the data? Taking into account possible expansion in the future. Should I use web services/WCF? RIA Services? Remoting? Or something else. What have people used in the past and what do you recommend? Thanks

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  • Simple ASP.Net MVC 1.0 Validation

    - by Mike
    On the current project we are working on we haven't upgraded to MVC 2.0 yet so I'm working on implementing some simple validation with the tools available in 1.0. I'm looking for feedback on the way I'm doing this. I have a model that represents a user profile. Inside that model I have a method that will validate all the fields and such. What I want to do is pass a controller to the validation method so that the model can set the model validation property in the controller. The goal is to get the validation from the controller into the model. Here is a quick example public FooController : Controller { public ActionResult Edit(User user) { user.ValidateModel(this); if (ModelState.IsValid) ....... ....... } } And my model validation signature is like public void ValidateModel(Controller currentState) What issues can you see with this? Am I way out to lunch on how I want to do this?

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  • trouble accessing non-static functions from static functions in AS3

    - by Dogmatixed
    I have a class containing, among other things, a drop down menu. With the aim of saving space, and since the contents of the menu will never change, I've made a static DataProvider for the whole class that populates each instances menu. I was hoping to populate the list with actual functions like so: tmpArr.push({label:"Details...", funct:openDetailsMenu, args:""}); and then assign tmpArr to the DataProvider. Because the DataProvider is static the function that contains that code also needs to be static, but the functions in the array are non-static. At first it didn't seem like a problem, because when the user clicks on a menu item the drop down menu can call a non-static "executeFunction(funct, args)" on its parent. However, when I try to compile, the static function setting up the DataProvider it can't find the non-static functions being passed. If the compiler would just trust me the code would work fine! The simple solution is to just pass strings and use a switch statement to call functions based on that, but that's big, ugly, inelegant, and difficult to maintain, especially if something inherits from this class. The simpler solution is to just make the DataProvider non-static, but I'm wondering if anyone else has a good way of dealing with this? Making the static function able to see its non-static brethren? Thanks.

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  • Deploying software on compromised machines

    - by Martin
    I've been involved in a discussion about how to build internet voting software for a general election. We've reached a general consensus that there exist plenty of secure methods for two way authentication and communication. However, someone came along and pointed out that in a general election some of the machines being used are almost certainly going to be compromised. To quote: Let me be an evil electoral fraudster. I want to sample peoples votes as they vote and hope I get something scandalous. I hire a bot-net from some really shady dudes who control 1000 compromised machines in the UK just for election day. I capture the voting habits of 1000 voters on election day. I notice 5 of them have voted BNP. I look these users up and check out their machines, I look through their documents on their machine and find out their names and addresses. I find out one of them is the wife of a tory MP. I leak 'wife of tory mp is a fascist!' to some blogger I know. It hits the internet and goes viral, swings an election. That's a serious problem! So, what are the best techniques for running software where user interactions with the software must be kept secret, on a machine which is possibly compromised?

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  • Do MSDTC and disaster recovery go together?

    - by DevDelivery
    Our application writes to multiple Sql Server databases within a distributed transaction. The Ops guys are saying that this messes up their disaster recovery plan because while the transactions on the live tables may commit at the same time, the log shipping on the separate databases happen at slightly different times. So in in a disaster recovery situation, there will be a few partial transactions. Is there a method for maintaining separate but synced databases in DR? Or do we have to re-design to relatively independent databases (or a single database)?

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  • Migrating from CPython to Jython

    - by itsadok
    I'm considering moving my code (around 30K LOC) from CPython to Jython, so that I could have better integration with my java code. Is there a checklist or a guide I should look at, to help my with the migration? Does anyone have experience with doing something similar? From reading the Jython site, most of the problems seem too obscure to bother me. I did notice that: thread safety is an issue Unicode support seems to be quite different, which may be a problem for me mysqldb doesn't work and needs to be replaced with zxJDBC Anything else? Related question: What are some strategies to write python code that works in CPython, Jython and IronPython

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  • Visitor pattern and compiler code generation, how to get children attributes?

    - by LeleDumbo
    I'd like to modify my compiler's code generator to use visitor pattern since the current approach must use multiple conditional statement to check the real type of a child before generating the corresponding code. However, I have problems to get children attributes after they're visited. For instance, in binary expression I use this: LHSCode := GenerateExpressionCode(LHSNode); RHSCode := GenerateExpressionCode(RHSNode); CreateBinaryExpression(Self,LHS,RHS); In visitor pattern the visit method is usually void, so I can't get the expression code from LHS and RHS. Keeping shared global variables isn't an option since expression code generation is recursive thus could erase previous values kept in the variables. I'll just show the binary expression as this is the most complicated part (for now): function TLLVMCodeGenerator.GenerateExpressionCode( Expr: TASTExpression): TLLVMValue; var BinExpr: TASTBinaryExpression; UnExpr: TASTUnaryExpression; LHSCode, RHSCode, ExprCode: TLLVMValue; VarExpr: TASTVariableExpression; begin if Expr is TASTBinaryExpression then begin BinExpr := Expr as TASTBinaryExpression; LHSCode := GenerateExpressionCode(BinExpr.LHS); RHSCode := GenerateExpressionCode(BinExpr.RHS); case BinExpr.Op of '<': Result := FBuilder.CreateICmp(ccSLT, LHSCode, RHSCode); '<=': Result := FBuilder.CreateICmp(ccSLE, LHSCode, RHSCode); '>': Result := FBuilder.CreateICmp(ccSGT, LHSCode, RHSCode); '>=': Result := FBuilder.CreateICmp(ccSGE, LHSCode, RHSCode); '==': Result := FBuilder.CreateICmp(ccEQ, LHSCode, RHSCode); '<>': Result := FBuilder.CreateICmp(ccNE, LHSCode, RHSCode); '/\': Result := FBuilder.CreateAnd(LHSCode, RHSCode); '\/': Result := FBuilder.CreateOr(LHSCode, RHSCode); '+': Result := FBuilder.CreateAdd(LHSCode, RHSCode); '-': Result := FBuilder.CreateSub(LHSCode, RHSCode); '*': Result := FBuilder.CreateMul(LHSCode, RHSCode); '/': Result := FBuilder.CreateSDiv(LHSCode, RHSCode); end; end else if Expr is TASTPrimaryExpression then if Expr is TASTBooleanConstant then with Expr as TASTBooleanConstant do Result := FBuilder.CreateConstant(Ord(Value), ltI1) else if Expr is TASTIntegerConstant then with Expr as TASTIntegerConstant do Result := FBuilder.CreateConstant(Value, ltI32) else if Expr is TASTUnaryExpression then begin UnExpr := Expr as TASTUnaryExpression; ExprCode := GenerateExpressionCode(UnExpr.Expr); case UnExpr.Op of '~': Result := FBuilder.CreateXor( FBuilder.CreateConstant(1, ltI1), ExprCode); '-': Result := FBuilder.CreateSub( FBuilder.CreateConstant(0, ltI32), ExprCode); end; end else if Expr is TASTVariableExpression then begin VarExpr := Expr as TASTVariableExpression; with VarExpr.VarDecl do Result := FBuilder.CreateVar(Ident, BaseTypeLLVMTypeMap[BaseType]); end; end; Hope you understand it :)

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  • Why are floating point values so prolific?

    - by Kibbee
    So, title says it all. Why are floating point values so prolific in computer programming. Due to problems like rounding errors, and not being able to even accurately represent numbers such as 0.1, I really can't see how they got as far as they did. I understand that the computation is faster with floating point numbers, however, I can think of only a few cases that they actually the right data type would be using. If you sat back and think about every time you used a floating point value, how many times did you say, well, some error would be ok, as long as the result was a few microseconds faster. It really makes me think because Jeff was talking about NP completeness, and how heuristics give an answer that is kind of right. And well, computers shouldn't do that. They should give you the answer that is correct. Yet we see floating point values used in many applications where they are completely not valid. What really bugs me, isn't that floating point exists, but that in many languages, there isn't even a viable alternative, non-floating point, decimal value. A lot of programmers when doing financial applications have to fall back to storing the number of cents in an integer field. Which brings with it all kinds of other problems. Why do floats continue to be so prolific, even though they can't represent the real answer, and we expect computers to be accurate? [EDIT] Just to clarify, I was talking about Base 2 floating points, and not base 10 floating points. .Net offers the Decimal data type, which is a base 10 floating point value which offers a much better representation of the numbers we deal with on a daily basis in most computer programs. I find it hard to believe that even modern languages like Java don't support base 10 floating point values, unless you want to move into the realm of things like BigDecimal, which isn't really the right answer either in a lot of situations.

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  • Building a Drupal Newsletter Module for handling Newsletter Articles

    - by Michael T. Smith
    We're building a module for generating HTML for email newsletters. We've looked into using a few other modules (SimpleNews, MailChimp, among others), but due to various requirements, it'll be easier and better for us to build a custom solution. Being a new Drupal developer, I'm a bit worried about handling this in a "non-Drupal" way. That being said, my plan is to setup a vocabulary with Newsletters as a term and the actual Newsletters as sub-terms, like so: Newsletters (term) - Newsletter A (sub-term) - Newsletter B (sub-term) This has the added benefit of being able to organize where articles were published (besides just on the site.) The question, though, is how to handle the different Newsletter issues. I could go another level deeper in the vocabulary, like so: Newsletters (term) - Newsletter A (sub-term) - Issue - 2010-03-01 - Issue - 2010-03-02 - Newsletter B (sub-term) - Issue - 2010-03-01 - Issue - 2010-03-08 But I'm wondering if this is adding a bit too much complexity. Once I have this taxonomy setup, when the user went to add new newsletters it would also create a node (content type: newsletter), and when he/she went to add new issues, it would also create a node (content type: issue.) Those would then be the landing pages for that content. So, the question is is there a better way for handling this structure? Is this a Drupal-like solution?

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  • Java Singleton Pattern

    - by Spencer
    I'm used the Singleton Design Pattern public class Singleton { private static final Singleton INSTANCE = new Singleton(); // Private constructor prevents instantiation from other classes private Singleton() {} public static Singleton getInstance() { return INSTANCE; } } My question is how do I create an object of class Singleton in another class? I've tried: Singleton singleton = new Singleton(); // error - constructor is private Singleton singleton = Singleton.getInstance(); // error - non-static method cannot be referenced from a static context What is the correct code? Thanks, Spencer

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  • Why use Python interactive mode?

    - by mvid
    When I first started reading about Python, all of the tutorials have you use Python's Interactive Mode. It is difficult to save, write long programs, or edit your existing lines (for me at least). It seems like a far more difficult way of writing Python code than opening up a code.py file and running the interpreter on that file. python code.py I am coming from a Java background, so I have ingrained expectations of writing and compiling files for programs. I also know that a feature would not be so prominent in Python documentation if it were not somehow useful. So what am I missing?

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  • Constructor overloading in Java - best practice

    - by errr
    There are a few topics similar to this, but I couldn't find one with a sufficient answer. I would like to know what is the best practice for constructor overloading in Java. I already have my own thoughts on the subject, but I'd like to hear more advice. I'm referring to both constructor overloading in a simple class and constructor overloading while inheriting an already overloaded class (meaning the base class has overloaded constructors). Thanks :)

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  • Is this the correct way of speaking to a "Content Manager" Class?

    - by DeanMc
    I am creating a silverlight site. I am currently breaking out my ideas into pieces of functionality. One of the idea's I have is the concept of a content manager. This is essentially a UI control with 4 regions. Top, Bottom, Right & Left. I also have a collection of objects that are considered "Menu Items". These are controls that function as a way to navigate around, similar to links. The idea I have is to implement an IMenuItem interface. Among the standard pieces of information (Text, PageReference, etc) I was also going to hold a reference to the content manager. My idea behind this thinking is that I can pass the PageReference to a property on the ContentManager and then call a method which knows how to update the content manager accordingly. Is this the best way of implementing this or is their some sort of pattern for it?

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  • Build and render infinite hierarchical category tree from self-referential category table

    - by FreshCode
    I have a Categories table in which each category has a ParentId that can refer to any other category's CategoryId that I want to display as multi-level HTML list, like so: <ul class="tree"> <li>Parent Category <ul> <li>1st Child Category <!-- more sub-categories --> </li> <li>2nd Child Category <!-- more sub-categories --> </li> </ul> </li> </ul> Presently I am recursively rendering a partial view and passing down the next category. It works great, but it's wrong because I'm executing queries in a view. How can I render the list into a tree object and cache it for quick display every time I need a list of all hierarchical categories?

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  • How to "DRY up" C# attributes in Models and ViewModels?

    - by DanM
    This question was inspired by my struggles with ASP.NET MVC, but I think it applies to other situations as well. Let's say I have an ORM-generated Model and two ViewModels (one for a "details" view and one for an "edit" view): Model public class FooModel // ORM generated { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public string EmailAddress { get; set; } public int Age { get; set; } public int CategoryId { get; set; } } Display ViewModel public class FooDisplayViewModel // use for "details" view { [DisplayName("ID Number")] public int Id { get; set; } [DisplayName("First Name")] public string FirstName { get; set; } [DisplayName("Last Name")] public string LastName { get; set; } [DisplayName("Email Address")] [DataType("EmailAddress")] public string EmailAddress { get; set; } public int Age { get; set; } [DisplayName("Category")] public string CategoryName { get; set; } } Edit ViewModel public class FooEditViewModel // use for "edit" view { [DisplayName("First Name")] // not DRY public string FirstName { get; set; } [DisplayName("Last Name")] // not DRY public string LastName { get; set; } [DisplayName("Email Address")] // not DRY [DataType("EmailAddress")] // not DRY public string EmailAddress { get; set; } public int Age { get; set; } [DisplayName("Category")] // not DRY public SelectList Categories { get; set; } } Note that the attributes on the ViewModels are not DRY--a lot of information is repeated. Now imagine this scenario multiplied by 10 or 100, and you can see that it can quickly become quite tedious and error prone to ensure consistency across ViewModels (and therefore across Views). How can I "DRY up" this code? Before you answer, "Just put all the attributes on FooModel," I've tried that, but it didn't work because I need to keep my ViewModels "flat". In other words, I can't just compose each ViewModel with a Model--I need my ViewModel to have only the properties (and attributes) that should be consumed by the View, and the View can't burrow into sub-properties to get at the values. Update LukLed's answer suggests using inheritance. This definitely reduces the amount of non-DRY code, but it doesn't eliminate it. Note that, in my example above, the DisplayName attribute for the Category property would need to be written twice because the data type of the property is different between the display and edit ViewModels. This isn't going to be a big deal on a small scale, but as the size and complexity of a project scales up (imagine a lot more properties, more attributes per property, more views per model), there is still the potentially for "repeating yourself" a fair amount. Perhaps I'm taking DRY too far here, but I'd still rather have all my "friendly names", data types, validation rules, etc. typed out only once.

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