Question

我在post_save函数中有以下代码

@receiver(post_save)
def update_parent_location(sender, instance=None, created=False, **kwargs):
list_of_models = ('A', 'B', 'C')

if sender.__name__ in list_of_models:
    groups = instance.group_set.all()
    fields_to_update = tuple(field.lower() for field in list_of_models)

    for field in fields_to_update:
        parent = getattr(instance, field, None)
        if parent is not None:
            parent.groups.add(*groups)
            parent.save()

我怎么知道

parent.groups.add(*groups)

部分实际上是添加了一个新对象还是静默失败了？

Answer 1

您可以查询之前和之后的组计数，以查看是否有任何更改：

...
num_groups = parent.groups.count()
parent.groups.add(*groups)
if parent.groups.count() > num_groups:
   # Something was added
   parent.save()
...

如何判断django RelatedManager .add（）是否发现该对象已被添加？

1 个答案: