实体框架代码优先：如何转换从数据库返回的一组实体？

Question

I'm trying to figure out why this isn't working...

DomainModel

public class ModelEntities : DbContext
{
    public DbSet<Address> Addresses { get; set; }
}

Controller

public ViewResult List(int id)
{
    var db = new ModelEntities();
    var addresses = db.Addresses.Where(x => x.CustomerID == id).AsEnumerable();
    return View(entities.Cast<AddressVM>());
}

View

@model IEnumerable<WebUI.Models.AddressVM>
...

AddressVM

public class AddressVM
{
    public AddressVM(Address address) { Bind(address); }

    private void Bind(Address address)
    {
        // Mapping logic is defined here
    }

    public static explicit operator AddressVM(Address address)
    {
        return new AddressVM(address);
    }
}

Now, if I change the view to accept IEnumerable<DomainModel.Models.Address> and don't do the cast everything works as expected.

When I try and do the cast I get the following error:

Unable to cast object of type 'System.Data.Entity.DynamicProxies.Address_37444C79F0AB1E0A599C8797F37448F12213C5BCAC0611B4C1C8EFADDEFAA82C' to type 'WebUI.Models.AddressVM'.

In the controller, why is addresses a collection of dynamic proxies even after calling AsEnumerable() ? What do I have to do to get a collection of my domain model objects so that I can cast them to the view model?

Answer 1

I bet your misunderstanding the concept of cast. A cast means the AddressVM instance is an Address instance... which i assume it's not. You will probably have to "convert" or instantiate the AddressVM object from the Address object. try this :

public ViewResult List(int id)
{
    var db = new ModelEntities();
    var addresses = from a in db.Addresses.Where(x => x.CustomerID == id)
                    select new AddressVM(a);
    return View(addresses );
}

[edit] According Brian's answer , you can cast an object if there is an implicit conversion between your actual type and the target type.

Answer 2

You need to setup an explicit operator on your AddressVM if you want to be able to cast an Address to it. You might take a look at AutoMapper if you want to move data from a domain model to a view model fairly easily.