_query_constraints_hash

# File activerecord/lib/active_record/persistence.rb, line 1179
    def _query_constraints_hash
      if self.class.query_constraints_list.nil?
        { @primary_key => id_in_database }
      else
        self.class.query_constraints_list.index_with do |column_name|
          attribute_in_database(column_name)
        end
      end
    end