diff options
| -rwxr-xr-x | activerecord/lib/active_record/associations.rb | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb index 273c210d63..59eb437c45 100755 --- a/activerecord/lib/active_record/associations.rb +++ b/activerecord/lib/active_record/associations.rb @@ -121,7 +121,7 @@ module ActiveRecord # # Consider the following loop using the class above: # - # for post in Post.find(:all, :limit => 100) + # for post in Post.find(:all) # puts "Post: " + post.title # puts "Written by: " + post.author.name # puts "Last comment on: " + post.comments.first.created_on @@ -129,20 +129,23 @@ module ActiveRecord # # To iterate over these one hundred posts, we'll generate 201 database queries. Let's first just optimize it for retrieving the author: # - # for post in Post.find(:all, :limit => 100, :include => :author) + # for post in Post.find(:all, :include => :author) # # This references the name of the belongs_to association that also used the :author symbol, so the find will now weave in a join something # like this: LEFT OUTER JOIN authors ON authors.id = posts.author_id. Doing so will cut down the number of queries from 201 to 101. # # We can improve upon the situation further by referencing both associations in the finder with: # - # for post in Post.find(:all, :limit => 100, :include => [ :author, :comments ]) + # for post in Post.find(:all, :include => [ :author, :comments ]) # # That'll add another join along the lines of: LEFT OUTER JOIN comments ON comments.post_id = posts.id. And we'll be down to 1 query. # But that shouldn't fool you to think that you can pull out huge amounts of data with no performance penalty just because you've reduced # the number of queries. The database still needs to send all the data to Active Record and it still needs to be processed. So its no # catch-all for performance problems, but its a great way to cut down on the number of queries in a situation as the one described above. # + # Please note that because eager loading is fetching both models and associations in the same grab, it doesn't make sense to use the + # :limit property and it will be ignored if attempted. + # # == Modules # # By default, associations will look for objects within the current module scope. Consider: |