Rails Ruby on Rails → 2.x

Has Many + non default primary key loads incorrect data.

I assume this is probably also the case for other has_* relationships, but have not verified.

I have a has_many association from class Foo to class Bar, where, for this specific relationship, the primary key on Foo is not id, nor is the foreign key on Bar id.

class Foo
  has_many, :bars, :primary_key => 'a_non_standard_key_name', :foreign_key => 'another_non_standard_key_name'
end

The relationship is one way, I have no need to navigate from Bar back to Foo, but only call a_foo.bars.

This works fine when working with a single object, but breaks down when you want to do eager association preloading to avoid n+1 query problem of loading bars for many foos.

When performing the following you find that

f = Foo.find :all, :include => :Bar
f.bars = [SOMETHING_UNEXPECTED]

The reason is that ActiveRecord creates the preloading query based on the default primary key of Foo (normally id).

It queries for Bar.another_non_standard_key_name matching Foo.id not Foo.a_non_standard_key_name

This causes seriously unexpected behaviour, and could easily go unnoticed since no errors are thrown.

I have found the hook in ActiveRecord where this functionality should be included and monkey patched for my system, because I need it now. I can't vouch for it's correctness, but we have many many specs for our product and none of them have broken because of this.

I'm running frozen rails 2.2.2

vendor/activerecord/lib/active_record/association_preload.rb, line 221

Change

primary_key_name = reflection.through_reflection_primary_key_name

to

primary_key_name = reflection.options[:primary_key] || reflection.through_reflection_primary_key_name

Hope this helps someone!

Emma