Demonstrates a bug in mongoid many-to-many associations with string keys

mongoid.rb

class User
  include Mongoid::Document
  field :name
  references_and_referenced_in_many :accounts
end

class Account
  include Mongoid::Document
  field :name
  key :name
  references_and_referenced_in_many :users
end

user = User.create!(:name => 'andy')

# This screws up and sets the account key in the user to an ObjectID
# so you end up with the user looking like..
# "account_ids" : ["4d3eac6770e81283be000068"]
user.accounts.create!(:name => 'test')

# Doing it this way works as expected
# so the user ends up with something like...
# "account_ids" : ["test"]
account = Account.create!(:name => 'test')
account.users << user