Rails3 has_many：through和foreign_key在set：class_name中不起作用

Question

Hi, all

I need find friends activities:

SELECT `activities`.* FROM `activities` 
INNER JOIN `friendships` 
ON `activities`.user_id = `friendships`.friend_id 
WHERE ((`friendships`.user_id = 1))

My add this code to User Model:

has_many :friends_activities, 
         :class_name => 'Activity', 
         :through => :friendships, 
         :foreign_key => :user_id, 
         :source => :friend

But Rails return is:

SELECT `activities`.* FROM `activities` 
INNER JOIN `friendships` 
ON `activities`.id = `friendships`.friend_id 
WHERE ((`friendships`.user_id = 1))

I need :

`activities`.user_id = `friendships`.friend_id

But Now:

`activities`.id = `friendships`.friend_id

PS: My Tables:

create_table "activities", :force => true do |t|
     t.integer  "user_id"
     t.integer  "target_id"
     t.string   "target_type"
     t.string   "verb"
     t.datetime "created_at"
     t.datetime "updated_at"
end

create_table "friendships", :force => true do |t|
     t.integer  "user_id",    :null => false
     t.integer  "friend_id",  :null => false
     t.string   "state"
     t.datetime "created_at"
     t.datetime "updated_at"
end

Answer 1

I am not sure you can use the additional options on the has_many :through. According to the docs :

Specifies an association through which to perform the query. This can be any other type of association, including other :through associations. Options for :class_name, :primary_key and :foreign_key are ignored , as the association uses the source reflection.

[emphasis mine]

Answer 2

Your last resort might be:

has_many :friends_activities, 
         :class_name => 'Activity', 
         :finder_sql => Proc.new {
            %Q{
               SELECT `activities`.* FROM `activities` 
               INNER JOIN `friendships` 
               ON `activities`.user_id = `friendships`.friend_id 
               WHERE ((`friendships`.user_id = #{id}))

              }
          }

I'm sure there is a more elegant way to achieve this, but in the meantime this should do the work.