hi All,

I am using mongoid 3.1.4, and have run into an issue with how the ID of a relation from an embedded document to a top-level document is persisted to mongodb.

Let there be top-level documents Foo and Bar, and then an embedded document SubBar defined as follows.

class Foo
  include Mongoid::Document
end

class Bar
  include Mongoid::Document
  embeds_many :sub_bars
end

class SubBar
  include Mongoid::Document
  belongs_to :foo, inverse_of: nil
  embedded_in :bar
end

In the app, I have the line:

foo = Foo.new.save!
bar = Bar.new
bar.profiles.build(foo_id: foo.id)
bar.save!

The result is a mongodb document (faking the object ids below) in the bars collection

{_id: ObjectId("1"), sub_bars: [{_id: ObjectId("2"), foo_id: "3"}]}

However, running the same command in a rails c session produces a mongodb document in the bars collection like

{_id: ObjectId("1"), sub_bars: [{_id: ObjectId("2"), foo_id: ObjectId("3")}]}

I am wondering why in one case foo_id is a string, whereas in the second case, foo_id is an ObjectId. I would prefer the result be an ObjectId.

Thanks!
-Eric

PS - Note that the MOPED logs show the same $pushAll in the update command in both cases.

"$pushAll" => {"sub_bars" => [{_id => "1", foo_id => "3"}]}