Question

If I have something like this:

class Post < ActiveRecord::Base
  has_many :comments, :as => :commentable do
    def approved
      find(:all, :conditions => {:approved => true})
    end
  end
end

class Comment < ActiveRecord::Base
  belongs_to :commentable, :polymorphic => true
end

…when I do this, I get 2 hits to the database (not including finding the post :p):

post = Post.first
post.comments #=> [Comment1, Comment2...]
post.comments.approved #=> [Comment1, Comment7...]

It seems like it should just filter the current comments array in memory, no? Is it doing that? Reason I ask is because the console shows SELECT * FROM ... on post.comments.approved, even though I already called post.comments. Shouldn’t this be better optimized in ActiveRecord?

Answer 1

The AR executes a new query for any finder calls inside a association extension method.
You can refer to the cached result set by using self.

  has_many :comments, :as => :commentable do
    def approved
      # uses the cached result set
      self.select{|c| c.approved == true}
    end
  end