query.py 文件源码

def update(self, using=None, **kwargs):
    """
    Updates specified attributes on the current instance.
    """
    assert self.pk, "Cannot update an instance that has not yet been created."

    using = using or router.db_for_write(self.__class__, instance=self)

    for field in self._meta.fields:
        if getattr(field, 'auto_now', False) and field.name not in kwargs:
            kwargs[field.name] = field.pre_save(self, False)

    affected = self.__class__._base_manager.using(using).filter(pk=self.pk).update(**kwargs)
    for k, v in kwargs.iteritems():
        if isinstance(v, ExpressionNode):
            v = resolve_expression_node(self, v)
        setattr(self, k, v)
    if affected == 1:
        post_save.send(sender=self.__class__, instance=self, created=False)
        return affected
    elif affected == 0:
        return affected
    elif affected < 0:
        raise ValueError("Somehow we have updated a negative amount of rows, you seem to have a problem with your db backend.")
    else:
        raise ValueError("Somehow we have updated multiple rows, and you are now royally fucked.")