递归多对多关系的相关名称不起作用 [英] Related name for recursive many to many relationship not working

问题描述

class A(models.Model):
    pass

class B(models.Model):
   parents = models.ManyToManyField(A, related_name='children')


>>> A._meta.get_all_field_names()
['children', u'id']

>>> B._meta.get_all_field_names()
[u'id', 'parents']

我可以得到 a.children.all（）和 b.parents.all（）的模型实例的孩子和父母的集合

I can get the sets of children and parents of model instances with a.children.all() and b.parents.all()

class FK(models.Model):
    parent = models.ForeignKey('self', related_name='child')


>>> FK._meta.get_all_field_names()
['child', u'id', 'parent']

现在，任何 FK 实例都可以使用 fk.parent 和<$ c来获取其父项和子项。 $ c> fk.child

Any instance of FK will now be able to get both its parent and its child with fk.parent and fk.child

class M2M(models.Model):
    parents = models.ManyToManyField('self', related_name='children')

>>> M2M._meta.get_all_field_names()
[u'id', 'parents']

，就像我可以访问 a.children 和 fk.child 一样，我也可以访问 m2m.children 。

One would expect that, like I could access a.children and fk.child, I would also be able to access m2m.children. This seems to not be the case.

我如何访问 m2m.children ？

我正在使用Django 1.6.5。

I'm using Django 1.6.5.

以 Daniel Roseman的答案说，设置 symmetrical = False 可以解决此问题。在 Django票证中，解释为：

As Daniel Roseman's answer said, setting symmetrical=False solves the problem. In a Django ticket it is explained as:

对于父母/孩子，这种关系不是对称的-如果A是B的孩子，那么就不会得出A是B的父母的情况。

In the case of parent/child, the relationship isn't symmetrical - if A is a child of B, it doesn't follow that A is a parent of B.

使用 symmetrical = False ，在 related_name 中指定的反向关系为就像在外键情况下创建的一样：

With symmetrical=False, the reverse relation specified in the related_name is created just like in the foreign key case:

class M2M(models.Model):
    parents = models.ManyToManyField('self', related_name='children', symmetrical=False)

>>> M2M._meta.get_all_field_names()
[u'id', 'parents', children]


>>> parent.children.add(child)
>>> parent.children.all()  # returns QuerySet containing the child
>>> child.parents.all()    # returns QuerySet containing the parent

的QuerySet

推荐答案

您需要设置 symmetrical = False 。作为 ManyToManyField的文档说：

当Django处理此模型时，它会识别出其自身具有ManyToManyField，因此不会添加person_set属性到Person类。取而代之的是，ManyToManyField假定是对称的，也就是说，如果我是你的朋友，那么你就是我的朋友。

When Django processes this model, it identifies that it has a ManyToManyField on itself, and as a result, it doesn’t add a person_set attribute to the Person class. Instead, the ManyToManyField is assumed to be symmetrical – that is, if I am your friend, then you are my friend.

如果您不希望与以下对象的多对多关系对称自我，将对称设置为False。这将迫使Django为反向关系添加描述符，从而允许ManyToManyField关系是非对称的。

If you do not want symmetry in many-to-many relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToManyField relationships to be non-symmetrical.

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