Backing field type mismatch check is too aggressive

[rmja]

The check in MemberMapper.cs for type compatability between the backing field and the associated property it too aggressive. It is currently:

if (!fieldInfo.FieldType.GetTypeInfo().IsAssignableFrom(property.ClrType.GetTypeInfo()))
{
    throw new InvalidOperationException(
        Strings.BadBackingFieldType(fieldName, fieldInfo.FieldType.Name, entityType.Name, propertyName, property.ClrType.Name));
}

This does not allow for simple type conversion between the backing field and the domain property, which is useful when the store type does not exactly match the domain type.

public class ExampleEntity
{
    private int _foo; // Store type is int

    public ushort Foo { get { return (ushort)_foo; } } // Domain type is actually ushort, but the store does not support unsigned.
}

The backing field can in this case always hold the value of the property, and so it should also pass the check. Note that typeof(int).IsAssignableFrom(typeof(ushort)) is false.

[rowanmiller]

Triage We have a work item to properly support type conversion (#242). What you probably want to do here is have everything in the CLR type defined as ushort and just have EF do the conversion. In the meantime, you could expose a private property typed as int and have EF map to that.