# Eager loading not working well for me **URL:** \ **Category:** Rails\ **Created:** [March 27, 2007, 4:39am UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261 "2007-03-27T04:39:14Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [March 27, 2007, 4:39am UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/1 "2007-03-27T04:39:14Z")
Man my app is causing me so much grief lately. Okay let’s say I have: class Discussion has\_many :posts end class Post belongs\_to :discussion acts\_as\_tree end Then let’s say I grab a discussion object and try to eager load all of its posts: discussion = Discussion.find(:first, :include =\> [:posts]) Seems simple enough and it grabs an entire tree of posts. However: discussion.posts.first.children will run a MySQL query instead of (more smartly) simply accessing the already eager-loaded posts. I’m getting pretty aggravated. I’ve been trying to properly handle going about my app for ages and nothing seems to work optimally. Any ideas? More importantly: should I even bother. ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [March 27, 2007, 8:30am UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/2 "2007-03-27T08:30:53Z")
Eleo wrote: > discussion = Discussion.find(:first, :include =\> [:posts]) > > Seems simple enough and it grabs an entire tree of posts. However: > > discussion.posts.first.children > > will run a MySQL query instead of (more smartly) simply accessing the > already eager-loaded posts. To avoid a query you have to eager load all the levels you’ll be accessing: discussion = Discussion.find(:first, :include =\> {:posts =\> :children}) – We develop, watch us RoR, in numbers too big to ignore. ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [March 27, 2007, 12:23pm UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/3 "2007-03-27T12:23:19Z")
That doesn’t make any sense to me though. When I do Dicussion.find(:first, :include =\> [:posts]) I have effectively grabbed all the posts, including the children and those children and so on. All of the posts, including children, have the same discussion\_id, after all. Another problem with :include =\> {:posts =\> :children} is that it only grabs one level of children. I can make the include argument more complex but there’s no way to know how deep a tree is. I’ve found a better way to get children without queries is something like: discussion.posts.collect {|post| if post.parent\_id = num}.compact Which will grab the children of a certain parent. This of course only works if I indeed have an entire tree of posts pre-loaded. ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [March 27, 2007, 8:05pm UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/4 "2007-03-27T20:05:28Z")
Eleo wrote: > I’ve found a better way to get children without queries is something > like: > > discussion.posts.collect {|post| if post.parent\_id = num}.compact > > Which will grab the children of a certain parent. This of course only > works if I indeed have an entire tree of posts pre-loaded. OK, I didn’t realise discussion.posts contained every post in the discussion, rather than just the top-level posts. Perhaps you should use Better Nested Set: [http://opensource.symetrie.com/trac/better\_nested\_set/](http://opensource.symetrie.com/trac/better_nested_set/) This will allow you to fetch the posts in depth-first order, so you can render whole discussion trees without searching, sorting, or re-querying. – We develop, watch us RoR, in numbers too big to ignore. ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [April 2, 2007, 3:08am UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/5 "2007-04-02T03:08:35Z")
I am using better nested set right now, but I don’t see precisely how I’m supposed to render without searching/sorting/querying. As it is, foo.children or the like will still query the database. Can you elaborate on how this is supposed to work, please? ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [April 2, 2007, 5:27am UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/6 "2007-04-02T05:27:58Z")
Eleo wrote: > I am using better nested set right now, but I don’t see precisely how > I’m supposed to render without searching/sorting/querying. As it is, > foo.children or the like will still query the database. Can you > elaborate on how this is supposed to work, please? Fetch all posts using discussion.posts.find(:all, :order =\> ‘lft’), then write a recursive rendering function that loops through these, watching for the parent\_id to change, increasing the depth by one when it changes to the id of the previous object, otherwise popping back up the levels until the parent\_ids match. – We develop, watch us RoR, in numbers too big to ignore. ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [April 9, 2007, 10:29pm UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/7 "2007-04-09T22:29:29Z")
This is the best I could come up with def show\_thread(posts, parent\_id = nil) #result = ‘’ result = “ \n” posts.each do |post| if post.parent\_id == parent\_id result += “- \n” result += render(:partial =\> ‘post’, :object =\> post) + “\n” result += show\_thread(posts, post.id) unless posts.select {|p| p.parent\_id == post.id }.empty? result += “ \n” end end result += ‘ ’ end It’s a massive waste of CPU ticks since it iterates through the array once for every item in the array and uses Array#select each time, but everything else I tried wasn’t working. The larger the thread, the dumber this method gets. If anyone has anything better please let me know. I tried something along the lines of what you suggested. While I figured out how to determine if the depth changed I ultimately couldn’t figure out how to close off all the tags properly. ---
**Author:** ![eleo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ea5d25/32.png) [@eleo](https://www.ruby-forum.com/u/eleo)\ **Post date:** [April 2, 2007, 5:49am UTC](https://www.ruby-forum.com/t/eager-loading-not-working-well-for-me/90261/8 "2007-04-02T05:49:23Z")
That makes sense (I think). Thanks.