Cross Posted from StackOverflow.

I'm likely missing something here, but it seems like this is a performance oversight. I first noticed this when looking at the query logs of Errbit and noticing hundreds of queries for the same objects.

It seems that all the children of a has_many relation don't have a reference back to their parent object after being loaded through the relation. i.e. accessing parent.children.map &:parent will get the parent from the DB _once for each child_ instead of being setup with the in-memory copy of parent

Example:

Using a very simple belongs_to / has_many setup:

    class Person
      include Mongoid::Document
      field :name
      has_many :posts, :inverse_of => :person
    end
                                             
    class Post
      include Mongoid::Document
      field :text
      belongs_to :person, :inverse_of => :posts
    end

Then, in the Rails console, a simple demonstration:

Loading development environment (Rails 3.2.12)
[1] pry(main)> tom = Person.create(:name => 'Tom')
[2] pry(main)> tom.posts.create(:text => 'stuff')
[3] pry(main)> tom.posts.create(:text => 'other stuff')
[4] pry(main)> Person.first.posts.map

=> [50687740, 50719060]

Note that last line, each person reference points to a different ruby object. I'm using ruby's object_id attribute to highlight the fact that these are literally different objects and this requires two round-trips to the database.

Why isn't the parent relation just a reference to the parent object after loading through the has_many relation?