实体框架v4 - >需要POCO和实体的一些帮助

Question

I'm using EF4 and I've got two entities that I wish to map to the same POCO . I'm not sure how I can do this.

Entity 1 → Foo (this represents a table FOO in the db)
POCO → Foo

Entity 2 → FooView (this represents a view FooView in the db)
POCO → Foo

I understand that I need to do something like

IObjectSet<Foo> _foos = CreateObjectSet<Foo>();

// Note spelling of the Entity.
IObjectSet<Foo> _foosView = CreateObjectSet<Foo>("FooViews"); 

But when i try this, it does compile, but it fails with the following exception:

System.ArgumentException: System.ArgumentException: The specified entity type, 'MyProject.Core.Foo', does not match the type 'EntityFramework.SqlServerModel.FoosView' from the EntitySet 'FoosViews'.

Any suggestions?

Answer 1

• How to: Define a Model with Multiple Entity Sets per Type
• How to: Add an Object to a Specific Entity Set

Here is a checklist of things to look for:

1. Your Storage Model should have:
   1. Two EntitySets : Foo and FooView
   2. Two EntityTypes : Foo and FooView
2. Your Conceptual Model should have:
   1. Two EntitySets : Foo and FooView - both with an EntityType set to ModelName.Foo
   2. One EntityType : Foo
3. Your Mapping should have two EntitySetMappings :
   1. Foo with one EntityTypeMapping ("ModelName.Foo") with one MappingFragment ("Foo")
   2. FooView with one EntityTypeMapping ("ModelName. Foo ") with one MappingFragment ("FooView")

You should new be able to execute the following:

Foo foo = new ModelEntities()
    .CreateObjectSet<Foo>("FooView")
    .First();

You can give yourself a headstart by doing the following:

1. Add Foo and FooView to your model
2. In the Mapping Details of Foo click Add a Table or View and select FooView
3. Delete FooView from your model
4. Save the model and open it in the XML editor
5. ( pre-RTM ) Find <EntityType Name="FooView"> in <StorageModels> and remove any incorrect entries from <Key> (it should match <EntityType Name="Foo"> )
6. Remove the <EntityTypeMapping Name="IsTypeOf(Foo)" /> and <EntityTypeMapping Name="IsTypeOf(FooView)" /> (they caused me errors)

As of beta 2, implementing the above will break the designer

Answer 2

In NHibernate, one should solve this using Projections. So, I think that there must exists something similar like that in the Entity Framework. I've googled a bit, and I came accross this:

• Object Queries (Entity Framework)