has_and_belongs_to_many or has_many for user/group relationship?

Question

I'm working on a Rails 3.1 app that has the following models:

User:

class User < ActiveRecord::Base
  has_and_belongs_to_many :groups
  has_many :ownerships, :class_name => 'Group'
end

Group:

class Group < ActiveRecord::Base
  has_and_belongs_to_many :users
  has_one :owner, :class_name => 'User'
end

There's a join table between them, and the groups table also has a "user_id" column. I would expect to be able to write this in my groups_controller.rb

@group = Group.find(params[:id])
foo = @group.owner

but when I do I'm presented with the following error:

Mysql2::Error: Unknown column 'users.group_id' in 'where clause': SELECT  `users`.* FROM `users`  WHERE `users`.`group_id` = 1 LIMIT 1

I don't understand why it's even looking for that column. Any help would be appreciated!

Answer 1

make sure your groups table has a user_id or owner_id column and try this:

  class Group < ActiveRecord::Base
    has_and_belongs_to_many :users
    belongs_to :owner, :class_name => 'User'
  end