In Rails: how do I create a many-to-many relationship where both models have teh join key?

Question

I have models A and B. Both have the magic column. If a record a from A and a b from B have the same magic, then they are related. Many records from A and B may have the same magic.

Is there a way to express this belongs_to_many sort of thing in my Rails models? How?

Answer 1

There's a high value in following the Rails way, and what you're trying to do isn't the standard way of doing this.

The Rails Way: You should create a has-and-belongs-to-many relationship using an intermediate model and table, as described in the Rails Guides website.

But if you insist...: Try this:

# model_a.rb
class ModelA < ActiveRecord::Base
  has_many :model_bs, class_name: 'ModelB',
                      foreign_key: :magic,
                      primary_key: :magic
end

# model_b.rb
class ModelB < ActiveRecord::Base
  has_many :model_as, class_name: 'ModelA',
                      foreign_key: :magic,
                      primary_key: :magic
end

I haven't tested this, but I am fairly certain that it would work.

Final words... Don't do it! Follow the Rails way. :)