Ruby on Rails

Ok... I had no idea. I always thought that if you have an
includes,that will automatically resolve to a join because otherwise
this might result in the N+1 problem. I guess I need to read up about
it some more.

One final question: when I return some_user.messages(another_user.id)
to json from my controller, I don't get the from_user and the to_user:
format.json { render :json => { :conversation => @messages.as_json } }
returns
{"conversation":[{"message":
{"created_at":"2012-02-25T20:21:01Z","from_user_id":1,"id":
2,"message":"lion king","to_user_id":3,"updated_at":null}},{"message":
{"created_at":"2012-02-25T20:21:01Z","from_user_id":3,"id":
9,"message":"this is ninth","to_user_id":1,"updated_at":null}}]}

How can I force the from_user and to_user as part of each "message"?
(I guess I could have them returned as separate tags at the same level
as "conversation", but I was wondering if there's a way to do it
inside "message", e.g. {"message":
{created_at:...","id":"1","from_user":{"name":"Bob","age":"20",
etc.}}})

Thanks so much for all the help!

On Apr 2, 8:55 am, Frederick Cheung <frederick.che...@gmail.com>
wrote:
> On Apr 2, 3:14 am, jenna_s <jenna.sim...@gmail.com> wrote:
>
> > 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?
>
> This is how include works by default. The loaded users are wired up to
> the message objects for you. There is one query per association, so
> you get the most benefit when there are multiple messages. The fact
> that it takes multiple queries (or even whether you use :include at
> all) has no effect on what the serialised json will look like.
>
> You can force AR to use a joins based include strategy via eager_load
> if you really want it to. (but like i said whether stuff is eagerly
> loaded or not doesn't impact the generated json)
>
> Fred
>
>
>
>
>
>
>
>
>
> > 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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