class Foo
  include Mongoid::Document
  embeds_many :bars
end
 
class Bar
  include Mongoid::Document
  embedded_in :foo
 
  field :name, :type => String
end
 
f = Foo.new
f.bars.build(:name => "Building")
f.save()

# This is what was fixed in MONGOID-4202
f.bars.where(:name => {:$not => /build/}).count
=> 1

# But these two should definitely == 1
f.bars.where(:$and => [{:name => {:$not => /build/}}]).count
=> 0

f.bars.where(:$or => [{:name => {:$not => /build/}}]).count
=> 0