:include doesn't work with belongs_to

rubyonrails-talk
1

I'm having issues getting :include to eagerly load data in a "belongs_to" association. Here's the breakdown:

Users have friends and an avatar image. If I am loading all the user's friends I want to also eagerly load the images for those users in the same SQL query -- instead of 1 query per friend, which adds up quickly. Here are my models:

Image     belongs_to :imageable, :polymorphic => true

User     has_many :images, :as => :imageable     has_many :friends, :include => :user,

Friend     # The user     belongs_to :owner_user,                      :class_name => "User",                      :foreign_key =>"user_id",

    # The friend     belongs_to :user,                      :class_name => "User",                      :foreign_key => "friend_id",                      :include => :images

As you can see I use :include on User#friends for "user" and then on Friend#user for "images". My thinking is, when accessing User#friends, rails will eagerly load the User object for each friend and all the images for that user.

friend -> user -> images

Currently the first part works (friend -> user), but it does not query for the images at the same time. So when I list all a user's friends with their avatars I get a lot of SQL queries.

What am I doing wrong? How can I optimize this?

2

Is there any work around that you can think of?

Thanks! Jeremy

3

I thought the known problem was the other way round?

ie if I'm loading some Images and i want to include :imageable then we're stuck (because we don;t know which tables to join on, and even if you do it would probably be rather ineffecient. (There is a patch out there (blowing my own horn for a second: http://dev.rubyonrails.org/ticket/9640), which does address this (although mainly as a side effect of completely replacing :include)). You can get this by hand: give the array of things, find the distinct types and do one query per type.

In this case you do get a warning about not being able to :include the polymorphic association. I thought the other way round was ok though. The code in associations.rb certainly looks like it's trying to handle it.

Fred

4

OK, so using polymorphic is what breaks this? So should is it more efficient to have different Models for different image types? I'll also go checkout your solution right now.