Question

I am trying to use a common EntityTypeConfiguration class to configure the primary key for all of my entities, so that each derived configuration class does not repeat itself. All of my entities implement a common interface IEntity (which says that each entity must have an Id property of type int).

My configuration base class looks like this:

public class EntityConfiguration<TEntity> : EntityTypeConfiguration<TEntity>

    where TEntity : class , IEntity {

    public EntityConfiguration() {

        HasKey( e => e.Id );

        Property( e => e.Id ).HasDatabaseGeneratedOption( DatabaseGeneratedOption.Identity );

    }

}

Each entity then has it’s own specific configuration class extending this one like this:

public class CustomerConfiguration : EntityConfiguration<Customer> {

    public CustomerConfiguration() : base() {

        // Entity specific configuration here

    }

}

It compiles fine, but the problem I am having is that at runtime I get the following Exception being raised when EF 4.1 RC tries to create the model:

System.InvalidOperationException was
unhandled Message=The key component
‘Id’ is not a declared property on
type ‘Customer’. Verify that it has
not been explicitly excluded from the
model and that it is a valid primitive
property. Source=EntityFramework

If I change the CustomerConfiguration class to extend from EntityTypeConfiguration<Customer> and repeat the primary key configuration then it works fine, but I lose the ability to share common configuration (DRY principal is the motivation).

• Am I doing something wrong here?
• Is there another way to share common configuration between entities?

For reference here are the other classes involved:

public interface IEntity {

    int Id { get; set; }

}

public class Customer : IEntity {

    public virtual int Id { get; set; }

    public virtual string name { get; set; }

}

Thanks!

Answer 1

I do not think that you need to go through all of this. EF 4.1 Code First uses a lot of convention over configuration and via this, the Id property of an entity is configured as the primary key. So by implementing the IEntity interface on your entities you are setting them up with the Id as the primary key.

Here is a link to the ADO.NET Team Blog that explains how the primary key convention works – Conventions for Code First