Entity Framework Cardinality Issue on a 0…1 Association

Question

I have database tables that look like this:

A Task can be mapped to a Module, or not mapped at all (0...1). I'm using Entity Framework database-first, and when I generated the model from the database, the Task entity came through with Modules as a collection (0 or more). So I opened up my EDMX and changed the "Modules" navigation property on Task to 0...1.

Now, when I attempt to compile, I get this error:

Error 3003: Problem in mapping fragments starting at line 1241:Given the cardinality of Association End Member Task, it should be mapped to key columns of the table TaskModule. Either fix the mapping or change the multiplicity of this end.

I don't understand what I need to do to fix this. I've looked at the association details and can't see the issue. I know I'm probably missing something stupid, but am totally stuck. Association properties:

Visual Studio 2010 SP1, Entity Framework 4.3.1.0, SQL Server 2008 R2.

Answer 1

One way to do this is to redefine the primary key for the TaskModule table. Instead of the primary key being (TaskId, ModuleName) it needs to be just (TaskId). Then do an update model from database and change any of the associations manually that didn't get picked up from that update.

Answer 2

Well your database schema is not correct with the description you give :

the TaskModule table implicates a many-to-many relationship, not a many-to-oneOrZero.

In edmx, many-to-many relation tables are not displayed, but they still exist in database.

So you should fix your database, or be happy with the relation proposed by EF !