UpdateModel() cannot assign new value to navigation property (entity reference)

This happens in ASP.NET MVC 2, .NET 4 (EF 4). My Address entity has a reference to the Post reference. Zip is the primary key of the Post entity. Another property in Post entity is CityName. In my views I allow users to change the CityName for the address which automatically (via jquery) loads up the corresponding Zip and stores it inside a hidden field.

When posted, both values are posted fine and binded to the Address's Post reference. But UpdateModel() fails to update them. It says that the Zip is part of the entity's Entity Key and cannot be changed.

I would gladly load up the Post entity by the new Zip and manually assign it to the existing Address but for a开发者_如何转开发ll other properties I stall want to rely on UpdateModel().

How can I achieve that? One would think that in EF4 stuff like this has been resolved..

By default the entity framework generated classes put restrictions on changing primary key values. This is good. You shouldn't change a PK for any reason at all. Changing PKs outside of add scenarios has pretty huge ramifications for state tracking and the general health of your system.

To solve this problem you want to tell UpdateModel not to update your primary keys using the exclude parameter.