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POASP.NET MVC Architecture : ViewModel by composition, inheritance or duplication?
 

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  1. POASP.NET MVC Architecture : ViewModel by composition, inheritance or duplication?
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    <p>I'm using ASP.NET MVC 3 and Entity Framework 4.1 Code First.</p> <p>Let's say I have a <code>User</code> entity :</p> <pre><code>public class User { public int Id { get; set; } public string Name { get; set; } public string Email { get; set; } public string Password { get; set; } } </code></pre> <p>When editing it in my <code>UserController</code> I want to add a <code>PasswordConfirmation</code> field and verify that <code>PasswordConfirmation == Password</code> </p> <h2>1. By composition</h2> <p>My first try was :</p> <pre><code>public class EditUserModel { [Required] public User User { get; set; } [Compare("User.Password", ErrorMessage = "Passwords don't match.")] public string PasswordConfirmation { get; set; } } </code></pre> <p>In this case the client side validation <del>works but</del> (<strong>Edit:</strong> client side validation working was a coincidence.) <strong>doesn't work</strong> and the <strong>server side validation fails</strong> with the following message : <em>Could not find a property named User.Password</em></p> <p><strong>Edit:</strong> I think the best solution, in this case, would be to create a custom <code>CompareAttribute</code></p> <p><strong>Implementing <code>IValidatableObject</code></strong></p> <pre><code>public class EditUserModel : IValidatableObject { [Required] public User User { get; set; } public string PasswordConfirmation { get; set; } public IEnumerable&lt;ValidationResult&gt; Validate(ValidationContext validationContext) { if(this.PasswordConfirmation != this.User.Password) return new[] { new ValidationResult("Passwords don't match", new[] { "PasswordConfirmation " }) }; return new ValidationResult[0]; } } </code></pre> <p>In this case the <strong>server side validation works</strong> but the <strong>client side validation doesn't work</strong> anymore. Implementing <code>IClientValidatable</code> seems a bit too complicated and I prefer not having client side validation in this case.</p> <h2>2. By inheritance</h2> <pre><code>public class EditUserModel : User { [Compare("Password", ErrorMessage = "Passwords don't match.")] public string PasswordConfirmation { get; set; } } </code></pre> <p>When trying to directly save <code>EditUserModel</code> using EF it doesn't work, I get some some error message about the <code>EditUserModel</code> metadata so I'm using <em>AutoMapper</em> to convert from <code>User</code> to <code>EditUserModel</code> and backwards. This solution <strong>works</strong> but it more complex because I have to convert from the model to the view model and backwards.</p> <h2>3. By duplication</h2> <p><em>(Suggested by Malte Clasen)</em></p> <p>The view model would have all the properties of the model plus additional ones. <em>AutoMapper</em> can be used to convert from one to another.</p> <pre><code>public class EditUserModel { public string Name { get; set; } public string Email { get; set; } public string Password { get; set; } [Compare("Password", ErrorMessage = "Passwords don't match.")] public string ConfirmPassword { get; set; } } </code></pre> <p>This is the solution I like the least because of code duplication (DRY) </p> <p><strong>Questions</strong></p> <p>What are the pros and cons of inheritance, composition and duplication in this case ?</p> <p>Is there a simple way to have both client side and server side validation without having to convert the model to the view model and backwards ?</p>
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