Question

In my Rails 3 project, I have a user model with a self referential join, through the follow model. I want to use this join table to find activity related to the followed user. I have almost everything set up correctly, except that the query generated by the join is totally ignoring the :primary_key option on the join model.

Here is the relevant schema for the relevant models:

  create_table "users", :force => true do |t|
    t.string   "email",                                 :default => "",    :null => false
    t.string   "first_name"
    t.string   "last_name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "follows", :force => true do |t|
    t.integer  "user_id"
    t.integer  "followed_user_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "activities", :force => true do |t|
    t.integer  "user_id"
    t.text     "body"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

Here’s the associations in the models

class User < ActiveRecord::Base
    has_many :follows
    has_many :followed_users, :through => :follows
  has_many :followed_activities, :through => :follows
    has_many :activities
end
class Follow < ActiveRecord::Base
    belongs_to :user
    belongs_to :followed_user, :class_name => "User"
    has_many :followed_activities, :primary_key => :followed_user, :foreign_key => :user_id, :class_name => "Activity"
end

The following work just fine:

u = User.first
u.follows # returns corresponding records from the follows table
u.followed_users # returns all users that u is following
u.followed_users.first.activities # returns all activity records corresponding to the first person the user is following
Follow.first.activities # same as the previous

However, the following just returns an empty array:

u.followed_activities

Here is the sql that is generated from the last statement:

  Activity Load (0.2ms)  SELECT `activities`.* FROM `activities` INNER JOIN `follows` ON `activities`.user_id = `follows`.id WHERE ((`follows`.user_id = 1))

The reason it isn’t working is because it is trying to join use ‘follows’.id as the primary key rather than ‘follows’.followed_user.

Is this a bug, or do I have to repeat the :primary_key declaration somewhere on the user model? I can’t find any mention anywhere in the Rails api, or anywhere else online.

Rails Version: 3.0.7

Answer 1

Justin, you have 2 associations called “followed_activities”. sure, they have different context (different models), but I’d like to ask you to try method inside the association block like this:

has_many :followed_users, :through => :follows do
  def activities
  end
end