Using Entities from an Entity Framework (v3.5) Model with Fluent NHibernate

Question

Hi all,

Using Microsoft's designer for the Entity Framework (v3.5), I have created an Entity Model (*.edmx) with a generated *.Designer.cs class. I can persist my objects to MS SQL Server using the model without any problems.

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I am new to NHibernate, and out of curiosity, I now would like to use my model with Fluent NHibernate and SQLite as database. I have read the Auto mapping article on the Fluent NHibernate wiki. I did adapt the Examples.FirstAutomappedProject and have adapted the ExampleAutomappingConfiguration to map my entities. (I used only the ShouldMap and IsId overrides). My entities are rather simple and do not contain explicit references to each other in the model.
Now, when I build the Session Factory, i get the following exception:

An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.

with an inner exception with the message

An association from the table XXX refers to an unmapped class: System.Data.EntityKey

None of my entities' properties are of type System.Data.EntityKey.

[global::System.Data.Objects.DataClasses.EdmEntityTypeAttribute(NamespaceName="MyStorageModel", Name="XXX")]
[global::System.Runtime.Serialization.DataContractAttribute(IsReference=true)]
[global::System.Serializable()]
public partial class XXX: global::System.Data.Objects.DataClasses.EntityObject
{
  //...
     [global::System.Data.Objects.DataClasses.EdmScalarPropertyAttribute(EntityKeyProperty=true, IsNullable=false)]
     [global::System.Runtime.Serialization.DataMemberAttribute()]
     public global::System.Guid XXXID
     {
        //...
     }
  //...
}

As you see, my entity classes are heavily decorated (by the used designer of course) with a attributes that probably refer to this type. Can this cause these troubles?

Answer 1

The problem probably is that your entity is inherited from EntityObject. EntityObject declares two public properties: EntityKey and EntityState. EntityKey is of type EntityKey and it is handled like association to class which you didn't provide to NHibernate. I think you will not be able to do this unless you use EF 4.0 and POCO which didn't inherit from EntityObject.

Answer 2

Using the database first EntityFramework code generation wizard will generate model classes that are tightly coupled to EntityFramework and that can't easily be used with NHibernate.

To make things worse, EntityFramework 3.5 doesn't really support POCO objects which would (likely) work with NHibernate. EF 4.0 has much better POCO support, but ultimately I'm not sure it would work as you want it to.

I would throw away the EntityFramework model classes and start over if you really want to work with Fluent NHibernate.

Here are some questions related to NHibernate model class code generation:

http://stackoverflow.com/questions/41752/nhibernate-generators http://stackoverflow.com/questions/1578341/what-is-the-best-code-generator-for-nhibernate