Not sure how to fix this weird Entity Framework (relationship/navigation) error

I keep getting the following error message when i try to save a poco entity, using Entity Framework as the OR/M :-

Entities in 'SqlServerContext.Foos' participate in the 'FK_Foos_Bahs' relationship. 0 related 'Bah' were found. 1 'Bah' is expected.

Ok - the error message makes sense -- but that is NOT what I modeled :( (or am trying to model). It's saying that if I wish to save a Foo, then I need 1 instance of a Bah. A 开发者_开发技巧Foo can exist without a Bah. The relationship should be 1 <-> 0-or-1 .. not 1 <-> 1.

Here's the model in EF ...

Can anyone see what I've done wrong?

Your model is probably wrong. At the moment you are saying that Bah is principal entity of many Foos. It is one-to-many relation not one-to-one. Also you defined Bah as mandatory in Foo because multiplicity on Bah is 1 not 0..1.

Looks like your relationship is back to front - your screen grab shows that 1 Bah has many Foos and Foo has exactly 1 Bah - it sounds like you need to swap the ends round so that 1 Foo can have many Bahs and Bah has exactly 1 Foo.

You can also do 0...1 to many relationships (each Bah can have many Foos, Bahs have 0 or 1 Foo), or 0...1 to 1 relationships. .Net will make nullable fields in the database and nullable properties in your model, and you'll be allowed to save data without the associations.

I know you're probably working with sensitive data hence the blanking out, but maybe if you swapped it to a more meaningful fake it'd be easier to understand what you're trying to do! Foo and Bah make a less intuitive demonstration than something equally sanitised like People and Pets or Hobbies or whatever.