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POEntityFramework throwing binding exception when casting to base type
 

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    <p><strong>Update</strong></p> <p>Apparently this was me just being wrong. the first example does not in fact work. I worked around this by serializing the object and then de-serializing it as the base class.</p> <hr> <p>I have some inconsistent issues from Entity Framework and am hoping someone could shed some light on why.</p> <p>This works:</p> <pre><code>public class ProductViewModel : Product { // Adds some select lists for View } public ActionResult Edit(ProductViewModel model) { if (ModelState.IsValid) { // Casting model to base type, EF has no issues. var product = (Product)model; Database.Entry(product).State = EntityState.Modified; Database.SaveChanges(); } return View(model); } </code></pre> <p>However this does not work:</p> <pre><code>public class OrderSurveyViewModel : tblSurvey { // adds select lists as ProductViewModel does } public ActionResult OrderSurvey(OrderSurveyViewModel model) { if(ModelState.IsValid){ // throws exceptions var survey = (tblSurvey)model; Database.tblSurvey.Add(survey); } } </code></pre> <p>The exception thrown is:</p> <blockquote> <p>Message: Mapping and metadata information could not be found for EntityType OrderSurveyViewModel</p> </blockquote> <p>Which makes sense since you can't change an objects type, casting it just 'hides' the types not belonging to that sub-type. But what I don't understand is why the top one works but the second one doesn't? Does the same mapping check simply not happen when you do Entry State Modified?</p> <p>Is there a way to still be able to do this without having to revert to simply creating a new base type and copying all of the field data?</p>
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    1. USsiva.k
    1. USsiva.k
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    1. COApart from your issue you're missing an important point by deriving view models from entities. The purpose of view models is to separate the domain model from the presentation layer by an intermediate controller or service layer. Of course it is tempting to use inheritance, but now you can never shape the entity model and VMs independently, so even database modifications may affect presentation code. Yes it is more work (although AutoMapper is a big help) but loose coupling is a prerequisite of maintainable code.
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      1. USGert Arnold
    2. COYou're absolutely right @GertArnold, in this specific case I actually needed my view model and my data model to always be identical, changes in the model are handled via Razor in the view. Since I couldn't guarantee the next person would update the view I need the new fields to show up as long as the EDMX file is updated. *cry* But it totally misses the point on separation of concerns.
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