Ruby-on-Rails: Multiple has_many :through possible?
Edit:
Rails 3.1 supports nested associations. E.g:
has_many :taskshas_many :assigments, :through => :taskshas_many :users, :through => :assignments
There is no need for the solution given below. Refer to this screencast for more details.
Original Answer
You are passing a has_many :through
association as a source for another has_many :through
association. I don't think it will work.
has_many :friends, :through => :friendships, :conditions => "status = #{Friendship::FULL}" has_many :friends_comments, :through => :friends, :source => :comments
You have three approaches to solving this issue.
1) Write an association extension
has_many :friends, :through => :friendships, :conditions => "status = #{Friendship::FULL}" do def comments(reload=false) @comments = nil if reload @comments ||=Comment.find_all_by_user_id(map(&:id)) end end
Now you can get the friends comments as follows:
user.friends.comments
2) Add a method to the User
class.
def friends_comments(reload=false) @friends_comments = nil if reload @friends_comments ||=Comment.find_all_by_user_id(self.friend_ids) end
Now you can get the friends comments as follows:
user.friends_comments
3) If you want this to be even more efficient then:
def friends_comments(reload=false) @friends_comments = nil if reload @friends_comments ||=Comment.all( :joins => "JOIN (SELECT friend_id AS user_id FROM friendships WHERE user_id = #{self.id} ) AS friends ON comments.user_id = friends.user_id") end
Now you can get the friends comments as follows:
user.friends_comments
All methods cache the results. If you want to reload the results do the following:
user.friends_comments(true)user.friends.comments(true)
OR better still:
user.friends_comments(:reload)user.friends.comments(:reload)
There is a plugin that solves your problem, take a look at this blog.
You install the plugin with
script/plugin install git://github.com/ianwhite/nested_has_many_through.git
Although this didn't work in the past, it works fine in Rails 3.1 now.