Entity Framework specify cardinality in a many to many relationship

Question

We have a many-to-many relationship, which we specify fluently like this:

Hasmay(A=>A.Bs).WithMany(B.As)

An "A" can have zero or more "B"'s. An "B" must have one or more "A"'s.

Is there a way to specify the cardinality for the "As" in "B"?

Answer 1

No, because under the hood it's a 1-n-1 association. That is, A has zero, one, or many AB junction records, and AB always has one B (and always one A ).

So we're dealing with the rules of 1-n associations. There is no way to enforce a 1 - 1 ..n association (ie a parent must have at least one child), at least not in DDL. Consequently there is no way to enforce 1..n - 1..m associations. It's always 0..n - 0..m. Only by business logic you can enforce mandatory associations.