DataMapper: one-to-many relationship with custom name?

Question

I'm trying to build a small model consisting of two entities. For the purposes of this question, call them A and B. A has a one-to-many relationship to several Bs; this means that each B belongs_to an A.

In this particular case, I'd like to call the relationship from B back to A something other than a. I think I got close with the following:

class A
    include DataMapper::Resource
    property :id, Serial
    has n, :bs
end

class B
    include DataMapper::Resource
    property :id, Serial
    belongs_to :owner, 'A'
end

The important bit here is the belongs_to :owner, 'A' line in B. With this, I can successfully:

• Create and save an instance of A
• Query that A for its bs and get an empty array back
• Create an instance of B, assigning its owner to be the A I made earlier

However, when I go to save that instance of B, I run into trouble – calling save returns false. If I print the B, I see that it has two attributes: one called owner_id and another called a_id.

What else do I need to do with this model to rename the relationship from B back to A? Is such a rename even possible?

Answer 1

Figured it out. The owning entity (A) needs to explicitly specify the child keys that it wants created for the relationship:

class A
    include DataMapper::Resource
    property :id, Serial
    has n, :bs, :child_key => [ 'owner_id' ]
end

class B
    include DataMapper::Resource
    property :id, Serial
    belongs_to :owner, 'A'
end

With this change, I only see one relationship attribute created on B, and I'm able to save instances of B that I create.