ActiveRecord-2.2.2, association preloading, joins and order parameter weirdness

rubyonrails-talk
1

Hello RoR Groupies,

I'm seeing some weird ActiveRecord-2.2.2 SQL generation when doing eager association/preloading and using joins and ordering by said join table.

Here's an example:

class Photo < ActiveRecord::Base end

class User < ActiveRecord::Base   has_one :headshot, :class_name => "Photo" end

class Mail < ActiveRecord::Base   belongs_to :user end

Mail.find(:all,    :joins => "INNER JOIN users u ON u.id = mails.user_id",   :conditions => "mails.user_id=1",   :include => { :user => :headshot },   :order => "u.name")

Now, the following SQL will be generated for the above statement:

SELECT `mails`.`id` AS t0_r0, `mails` ... `users`.`id` AS t1_r0, .. `photos`.`id` AS t2_r0, FROM `mails` LEFT OUT JOIN `users` ON `users`.id = `mails`.user_id LEFT OUTER JOIN `photos` ON photos.user_id = users.id INNER JOIN users u ON u.id = mails.user_id WHERE (mails.user_id=1) ORDER BY u.name

Notice the LEFT OUTER join being added. While the SQL is okay and gets the right results, its less than efficient.

HOWEVER, if the order parameter is changed to NOT include u.name (say use mails.created_at instead as an example), or removed completely, ActiveRecord will generate 3 SQL statements.

SELECT * FROM `mail` NNER JOIN users u ON u.id = mails.user_id WHERE (mails.user_id=1) ORDER BY u.name SELECT * FROM `users` WHERE ... SELECT * FROM `photos` WHERE ...

The two questions I have are:

1) Why AR is paying attention to what's in the ORDER parameter and choosing the eager loading strategy based from that?

2) Is there any way I can force AR to choose the loading strategy? Or at least tell it not to do a LEFT OUTER JOIN.

-- Michael

2

The two questions I have are:

1) Why AR is paying attention to what's in the ORDER parameter and choosing the eager loading strategy based from that?

Mainly for backwards compatibility AR falls back to the join based include stuff when it thinks you're referencing (in conditions, order etc..) something from one of the included tables, because clearly having a condition on a table you don't join won't work. In 2.2 it's not smart enough to scan the joins clause to see that references to those tables are OK (it is in rails 2.3).

2) Is there any way I can force AR to choose the loading strategy? Or at least tell it not to do a LEFT OUTER JOIN.

Not that I know of

Fred