Django查询单下划线是否像双下划线一样? [英] Django query single underscore behaving like double underscore?

问题描述

我最近在代码中打了一个错字，发现我得到了相同的行为，所以我想知道Django查询中单下划线和双下划线之间的区别是什么.

I made a typo in my code recently and noticed that I got the same behavior, so I was wondering what the difference between single and double underscores are in django queries.

>>> underscore = MyModel.objects.filter(foreign_key_id=var)
>>> double_underscore =  MyModel.objects.filter(foreign_key__id=var)
>>> underscore == double_underscore
False
>>> list(underscore) == list(double_underscore)
True

我不确定正在使用哪种相等方法比较查询集，但是当我转换为python列表时，会发现其中包含的元素完全相同.有人对这里发生的事情有一些了解吗?

I'm not sure what equality method is being used to compare the querysets, but when I convert to python lists I find exactly the same elements contained within. Does anyone have some insight into what's going on here?

推荐答案

这两个字段恰好都存在.

Those two fields just happen to both exist.

foreign_key_id是在MyModel对象上自动创建的列，而foreign_key__id是外键表本身上的ID.

foreign_key_id is an automatically created column on the MyModel object, whereas foreign_key__id is the ID on the foreign key table itself.

这些值都将相同.

MyModel1.foreign_key_id == 5  # this is stored on the model
                              # and does not require a lookup.
MyModel1.foreign_key.id == 5  # this is stored on the target table
                              # and requires a DB hit. 

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