给出这两个模型：
class Item(models.Model):
timestamp = models.DateTimeField()
class Source(models.Model):
items = models.ManyToManyField(Item,related_name="sources")
我可以在给定的时间之前使用以下内容找到所有的Source的项目：
source.items.filter(timestamp__lte=some_datetime)
如何有效地删除与该查询匹配的所有项目？我想我可以尝试这样的事情：
items_to_remove = list(source.items.filter(timestamp__lte=some_datetime)) source.items.remove(*items_to_remove)
但这似乎不好
解决方法
我认为你的钱是正确的,除非你不需要转换成清单.
source.items.remove(*source.items.filter(*args))
remove / add方法如下所示
remove(self,*objs) add(self,*objs)
和文档http://www.djangoproject.com/documentation/models/many_to_many/
使用[p1,p2,p3]的形式添加多个示例,所以我会下注相同的删除,看到参数是一样的.
>>> a2.publications.add(p1,p3)
多一点挖掘,remove函数逐个迭代* obj,检查它是否是有效的模型,否则使用值作为PK,然后删除与pk__in的项目,所以我会说是的,最好的方法是首先查询您的m2m表,以删除对象,然后将这些对象传递给m2m管理器.
# 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",pk_set=old_ids)