Poor Ruby on Rails performance when using nested :include
- by Jeremiah Peschka
I have three models that look something like this:
class Bucket < ActiveRecord::Base
has_many :entries
end
class Entry < ActiveRecord::Base
belongs_to :submission
belongs_to :bucket
end
class Submission < ActiveRecord::Base
has_many :entries
belongs_to :user
end
class User < ActiveRecord::Base
has_many :submissions
end
When I retrieve a collection of entries doing something like:
@entries = Entry.find(:all,
:conditions => ['entries.bucket_id = ?', @bucket],
:include => :submission)
The performance is pretty quick although I get a large number of extra queries because the view uses the Submission.user object. However, if I add the user to the :include statement, the performance becomes terrible and it takes over a minute to return a total of 50 entries and submissions spread across 5 users. When I run the associated SQL commands, they complete in well under a second.
@entries = Entry.find(:all,
:conditions => ['entries.bucket_id = ?', @bucket],
:include => {:submission => :user})
Why would this second command have such terrible performance compared to the first?
