如何根据过滤器删除ManyToMany关系中的多个对象？ [英] How do I remove multiple objects in a ManyToMany relationship based on a filter?

问题描述

给定这两个模型：

class Item(models.Model):
    timestamp = models.DateTimeField()

class Source(models.Model):
    items = models.ManyToManyField(Item, related_name="sources")

我可以在给定时间之前使用以下内容找到所有的源项目：

I can find all of a Source's Items before a given time using this:

source.items.filter(timestamp__lte=some_datetime)

如何有效地删除所有的符合该查询的项目？我想我可以尝试这样的事情：

How do I efficiently remove all of the items that match that query? I suppose I could try something like this:

items_to_remove = list(source.items.filter(timestamp__lte=some_datetime))
source.items.remove(*items_to_remove)

但似乎不好。

请注意，我不想删除这些项目，因为它们也可能属于其他来源。我只想删除他们与具体来源的关系。

Note that I do not want to delete these items, since they may also belong to other Sources. I just want to remove their relationship with the specific source.

推荐答案

我认为你的钱正确，除了你不需要转换为列表。

I think you got it right on the money, except you don't need to convert to a list.

source.items.remove(*source.items.filter(*args))

删除 / 添加方法看起来像以下

The remove/add method looks like the following

remove(self, *objs)
add(self, *objs)

和文档 http://www.djangoproject.com/documentation/models/many_to_many/
使用以形式添加多个示例[p1，p2， p3] 所以我也会为删除下注，因为参数是一样的。

and the docs http://www.djangoproject.com/documentation/models/many_to_many/ use add multiple examples in the form of [p1, p2, p3] so I'd wager the same goes for remove, seeing as the arguments are the same.

>>> a2.publications.add(p1, p2, p3)

更多的挖掘，删除功能逐个迭代 * objs ，检查它是否是有效的模型，否则使用值作为PK，然后删除具有 pk__in ，所以我会说是的，最好的方法是首先查询你的m2m表，然后将这些对象传递给m2m管理器。

Digging in a little more, the remove function iterates over *objs one by one, checking if it's of the valid model, otherwise using the values as PK's, then deletes the items with a pk__in, so I'm gonna say yes, the best way is to query your m2m table first for objects to delete then pass in those objects into the m2m manager.

    # django.db.models.related.py
    def _remove_items(self, source_field_name, target_field_name, *objs):
        # source_col_name: the PK colname in join_table for the source object
        # target_col_name: the PK colname in join_table for the target object
        # *objs - objects to remove

        # If there aren't any objects, there is nothing to do.
        if objs:
            # Check that all the objects are of the right type
            old_ids = set()
            for obj in objs:
                if isinstance(obj, self.model):
                    old_ids.add(obj.pk)
                else:
                    old_ids.add(obj)
            if self.reverse or source_field_name == self.source_field_name:
                # Don't send the signal when we are deleting the
                # duplicate data row for symmetrical reverse entries.
                signals.m2m_changed.send(sender=rel.through, action="pre_remove",
                    instance=self.instance, reverse=self.reverse,
                    model=self.model, pk_set=old_ids)
            # Remove the specified objects from the join table
            db = router.db_for_write(self.through.__class__, instance=self.instance)
            self.through._default_manager.using(db).filter(**{
                source_field_name: self._pk_val,
                '%s__in' % target_field_name: old_ids
            }).delete()
            if self.reverse or source_field_name == self.source_field_name:
                # Don't send the signal when we are deleting the
                # duplicate data row for symmetrical reverse entries.
                signals.m2m_changed.send(sender=rel.through, action="post_remove",
                    instance=self.instance, reverse=self.reverse,
                    model=self.model, pk_set=old_ids)

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