:include doesn't work with belongs_to

Rails
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

Mozmonkey wrote:

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

I believe there is a known bug with eager loading and belongs_to. I just
can’t find the ticket in trac.

–
Josh S.
http://blog.hasmanythrough.com

3

Is there any work around that you can think of?

Thanks!
Jeremy

4

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

5

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.