instance method _update_record

# File activerecord/lib/active_record/persistence.rb, line 487
    def _update_record(attribute_names = @attributes.keys)
      attributes_with_values = arel_attributes_with_values_for_update(attribute_names)
      if attributes_with_values.empty?
        0
      else
        klass = self.class
        column_hash = klass.connection.schema_cache.columns_hash klass.table_name
        db_columns_with_values = attributes_with_values.map { |attr,value|
          real_column = column_hash[attr.name]
          [real_column, value]
        }
        bind_attrs = attributes_with_values.dup
        bind_attrs.keys.each_with_index do |column, i|
          real_column = db_columns_with_values[i].first
          bind_attrs[column] = klass.connection.substitute_at(real_column, i)
        end
        stmt = klass.unscoped.where(klass.arel_table[klass.primary_key].eq(id_was || id)).arel.compile_update(bind_attrs)
        klass.connection.update stmt, 'SQL', db_columns_with_values
      end
    end