module Mongoid::Criteria::Queryable::Mergeable

def prepare(field, operator, value)
  unless operator =~ /exists|type|size/
    value = value.__expand_complex__
    field = field.to_s
    name = aliases[field] || field
    serializer = serializers[name]
    value = serializer ? serializer.evolve(value) : value
  end
  selection = { operator => value }
  negating? ? { "$not" => selection } : selection
end