2-way associations

rubyonrails-talk
1

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

2

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

3

You're fretting over 0.000650 seconds. Please.

4

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.