Question

In Linq to SQL I could specify a relationship that didn’t have to depend on the foreign keys and pks existing in the database, useful for creating composite relationships like this:

public class Equipment_CableNormalised
{
    ...

    [Association(ThisKey = "EquipmentId,PortNumber", OtherKey = "EquipmentId,PortNumber", IsForeignKey = false)]
    public List<EquipmentPort> EquipmentPorts
    {
        get; set;
    }

}

This then generated the sql similar to " .. join EquipmentPorts EP on EP.EquipmentId = blah and EP.PortNumber = Blah".

Can I do the same sort of thing in EF4.1 (using annotations or fluent api)? I know you can specify composite keys and use the [Keys] and [ForeignKeys] attributes, but this relationship doesn’t map to keys…

Answer 1

How does the sample relation from your code works? I expect that EquipementId must be either PK or unique key (not supported in both L2S and EF) on one side because otherwise the relation could not exist (both one-to-one and one-to-many demands unique principal). Once it is PK on one side the port number is redundant.

Code first allows only mapping to keys. If you have existing database you can cheat it in your model and map new relations in the same way as you would map existing but you still have to follow simple rule – properties in principal are primary keys, properties in dependent entity are mapped as foreign keys.

If you want EF to generate DB for you, you will always have all relations in the database.