Rails - Feb 2008 - 2-way associations

Hello,

I was wondering if there is an easy way to handle this N+1 problem.

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post

  def full_name
    "comment on #{post.title} by #{author}"
  end
end

Now when I want a post with all its comments, I go:
p=Post.find(:first, :include => :comments)

queries:
Post Load Including Associations (0.000863)   SELECT posts."id" AS
t0_r0, posts."title" AS t0_r1, posts."body" AS t0_r2,
posts."eated_at"
AS t0_r3, posts."updated_at" AS t0_r4, comments."id" AS
t1_r0,
comments."post_id" AS t1_r1, comments."body" AS t1_r2,
coents."created_at" AS t1_r3, comments."updated_at" AS t1_r4
FROM
posts LEFT OUTER JOIN comments ON comments.post_id = posts.id

p.comments.first.full_name

queries:
Post Load (0.000650)   SELECT * FROM posts WHERE (posts."id" = 1)

It seems to me it''s a little dumb to re-get the post, since
it''s
already loaded and associated to this comment(since the comment was
loaded through the post''s association).
Ofcourse I could use Post.find(:first, :include => {:comments
=> :post}).
But it doesn''t feel right since Post is included twice.

Any "good" way to do this?

Thanks.
Mathijs
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> I was wondering if there is an easy way to handle this N+1 problem.
> 
> class Post < ActiveRecord::Base
>   has_many :comments
> end
> 
> class Comment < ActiveRecord::Base
>   belongs_to :post
> 
>   def full_name
>     "comment on #{post.title} by #{author}"
>   end
> end
> 
> Now when I want a post with all its comments, I go:
> p=Post.find(:first, :include => :comments)
> p.comments.first.full_name
> Any "good" way to do this?
Well I normally dislike putting text into models. If you want to use 
this for printing in a template, you can puts something liek this in a 
helper:

   def full_name(post)
     "comment on #{post.title} by #{post.comments.first.author}"
   end

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bluescreen303-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> 
> queries:
> Post Load Including Associations (0.000863)   SELECT posts."id"
AS
> t0_r0, posts."title" AS t0_r1, posts."body" AS t0_r2,
posts."eated_at"
> AS t0_r3, posts."updated_at" AS t0_r4, comments."id" AS
t1_r0,
> comments."post_id" AS t1_r1, comments."body" AS t1_r2,
> coents."created_at" AS t1_r3, comments."updated_at" AS
t1_r4 FROM
> posts LEFT OUTER JOIN comments ON comments.post_id = posts.id
> 
> p.comments.first.full_name
> 
> queries:
> Post Load (0.000650)   SELECT * FROM posts WHERE (posts."id" = 1)
> 
> 
> Thanks.
> Mathijs
I am quite surprised at your findings, I assumed that the association 
from comment to post would have been established with the first 
collection loading (post to comments).

I will have to try this on my machine tomorrow at work but I assumed 
that when an AR collection loads it components, the contained components 
automatically get the  container id..

ilan



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You''re fretting over 0.000650 seconds. Please.

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Like I said, this is just a basic ''proof of concept''.
Ofcourse in this case (almost empty db, sqlite locally) it doesn''t
matter at all, especially not with 1 comment.

And ofcourse putting text should be in a helper, this is just to
demonstrate the strange behavior, the actual case needs different
data(not text) from the parent object.

In real life situations this WILL hurt since it''s a N+1 problem.
If in my example a certain post has 10000 comments, it will generate
10001 queries just for this simple bit of code.


On 26 feb, 08:00, Ryan Bigg
<radarliste...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> You''re fretting over 0.000650 seconds. Please.
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