Question

We have a model Entry with an embedded Item:

class Entry
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::Spacial::Document
  embeds_many :items, cascade_callbacks: true
...

class Item
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::Spacial::Document
  embedded_in :entry
...

If i query mongo directly for an entry by item id:

{"items._id" : ObjectId("50536b18baa072000f000360")}

It returns the Entry:

505363b36181ce00020006b1
{“created_at”:”2012-09-14T17:04:51Z”,”items”:[{“_id”:”50536b1a2b17b3…

Yet when i query via Mongoid:

irb(main):002:0> Entry.where('items._id' => '50536b18baa072000f000360')[0]
=> nil

All other queries work (for other fields on items and for fields on entry). But not for id.

We’re running mongoid (2.4.12).

Answer 1

Apparently you have to wrap the ID in BSON::ObjectId(), so:

Entry.where('items._id' => BSON::ObjectId('50536b18baa072000f000360'))[0]

Otherwise mongo will sporatically not return the result.