Ruby on Rails

Hi Peter,

How did you know that?! Yes, indeed there are 3 SQL queries:

Message Load (0.5ms) SELECT `messages`.* FROM `messages` WHERE
(from_user_id = 3 AND to_user_id = '2' OR to_user_id = 3 AND
from_user_id = '2') ORDER BY created_at DESC LIMIT 1
User Load (0.4ms) SELECT `users`.* FROM `users` WHERE (`users`.`id` =
2)
User Load (0.5ms) SELECT `users`.* FROM `users` WHERE (`users`.`id` =
3)

Why is that? I really expected one SQL statement. In fact I need one
SQL statement since I need to serialize and respond to in JSON. How
can I fix it?

Thanks so much,
Jenna

On Mar 31, 1:56 pm, Peter Vandenabeele <pe...@vandenabeele.com> wrote:
> On Sat, Mar 31, 2012 at 10:28 PM, jenna_s <jenna.sim...@gmail.com> wrote:
> > Hi,
>
> > I'm having trouble with a simple users-messages setup, where users can
> > send messages to other users. Here's my class definition:
>
> > class Message < ActiveRecord::Base
> >  belongs_to :from_user, :class_name => 'User'
> >  belongs_to :to_user, :class_name => 'User'
> > end
>
> > class User < ActiveRecord::Base
> >  def messages(with_user_id)
> >    Message.where("from_user_id = :id AND to_user_id = :with_user_id
> > OR to_user_id = :id AND from_user_id = :with_user_id",
> >      { :id => id, :with_user_id => with_user_id })
> >      .includes(:from_user, :to_user)
> >      .order("created_at DESC")
> >  end
> > end
>
> > When I do some_user.messages(another_user.id), I want to retrieve the
> > conversation that some_user has with another_user. I do get back an
> > array of Messages, but it doesn't include the eager loading of
> > from_user and to_user.
>
> How many SQL queries do you see in the log for
>
> messages = some_user.messages(another_user.id)
>
> (I believe you should see 3 queries if from_user and to_user data
> is present).
>
> When asking later on:
>
> messages.first.from_user
>
> is it then launching an SQL for the individual from_user
> at that time?
>
> > What am I doing wrong? Am I forced to use
> > joins?
>
> It must be possible to get this working with .includes
> as you tried.
>
> HTH,
>
> Peter

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