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POMVC 3 Model Binding a Sub Type (Abstract Class or Interface)
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  1. POMVC 3 Model Binding a Sub Type (Abstract Class or Interface)
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    copied!<p>Say I have a Product model, the Product model has a property of ProductSubType (abstract) and we have two concrete implementations Shirt and Pants.</p> <p>Here is the source:</p> <pre><code> public class Product { public int Id { get; set; } [Required] public string Name { get; set; } [Required] public decimal? Price { get; set; } [Required] public int? ProductType { get; set; } public ProductTypeBase SubProduct { get; set; } } public abstract class ProductTypeBase { } public class Shirt : ProductTypeBase { [Required] public string Color { get; set; } public bool HasSleeves { get; set; } } public class Pants : ProductTypeBase { [Required] public string Color { get; set; } [Required] public string Size { get; set; } } </code></pre> <p>In my UI, user has a dropdown, they can select the product type and the input elements are displayed according to the right product type. I have all of this figured out (using an ajax get on dropdown change, return a partial/editor template and re-setup the jquery validation accordingly).</p> <p>Next I created a custom model binder for ProductTypeBase. </p> <pre><code> public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) { ProductTypeBase subType = null; var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int)); if (productType == 1) { var shirt = new Shirt(); shirt.Color = (string)bindingContext.ValueProvider.GetValue("SubProduct.Color").ConvertTo(typeof(string)); shirt.HasSleeves = (bool)bindingContext.ValueProvider.GetValue("SubProduct.HasSleeves").ConvertTo(typeof(bool)); subType = shirt; } else if (productType == 2) { var pants = new Pants(); pants.Size = (string)bindingContext.ValueProvider.GetValue("SubProduct.Size").ConvertTo(typeof(string)); pants.Color = (string)bindingContext.ValueProvider.GetValue("SubProduct.Color").ConvertTo(typeof(string)); subType = pants; } return subType; } } </code></pre> <p>This binds the values correctly and works for the most part, except I lose the server side validation. So on a hunch that I am doing this incorrectly I did some more searching and came across this answer by Darin Dimitrov:</p> <p><a href="https://stackoverflow.com/questions/4012217/asp-net-mvc-2-binding-to-abstract-model">ASP.NET MVC 2 - Binding To Abstract Model</a></p> <p>So I switched the model binder to only override CreateModel, but now it doesn't bind the values.</p> <pre><code>protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType) { ProductTypeBase subType = null; var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int)); if (productType == 1) { subType = new Shirt(); } else if (productType == 2) { subType = new Pants(); } return subType; } </code></pre> <p>Stepping though the MVC 3 src, it seems like in BindProperties, the GetFilteredModelProperties returns an empty result, and I think is because bindingcontext model is set to ProductTypeBase which doesn't have any properties. </p> <p>Can anyone spot what I am doing wrong? This doesn't seem like it should be this difficult. I am sure I am missing something simple...I have another alternative in mind of instead of having a SubProduct property in the Product model to just have separate properties for Shirt and Pants. These are just View/Form models so I think that would work, but would like to get the current approach working if anything to understand what is going on...</p> <p>Thanks for any help!</p> <h1>Update:</h1> <p>I didn't make it clear, but the custom model binder I added, inherits from the DefaultModelBinder</p> <h1>Answer</h1> <p>Setting ModelMetadata and Model was the missing piece. Thanks Manas!</p> <pre><code>protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType) { if (modelType.Equals(typeof(ProductTypeBase))) { Type instantiationType = null; var productType = (int)bindingContext.ValueProvider.GetValue("ProductType").ConvertTo(typeof(int)); if (productType == 1) { instantiationType = typeof(Shirt); } else if (productType == 2) { instantiationType = typeof(Pants); } var obj = Activator.CreateInstance(instantiationType); bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, instantiationType); bindingContext.ModelMetadata.Model = obj; return obj; } return base.CreateModel(controllerContext, bindingContext, modelType); } </code></pre>
 

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