Django中同一模型的多个多对多关系

Question

鉴于以下模型具有两个多对多关系:

class Child(models.Model):
    name = models.CharField(max_length=80)

class Foo(models.Model):
    bar = models.ManyToManyField(Child)
    baz = models.ManyToManyField(Child)

这给出了错误:

accounts.foo: Accessor for m2m field 'bar' clashes with related m2m field 'Child.foo_set'. Add a related_name argument to the definition for 'bar'.
accounts.foo: Accessor for m2m field 'baz' clashes with related m2m field 'Child.foo_set'. Add a related_name argument to the definition for 'baz'.

精细; 我不需要向后的关系.根据相关名称的Django文档(据我所知,它只在ForeignKey下),我可以设置related_name="+"和不创建后向关系:

class Child(models.Model):
    name = models.CharField(max_length=80)

class Foo(models.Model):
    bar = models.ManyToManyField(Child, related_name="+")
    baz = models.ManyToManyField(Child, related_name="+")

这不起作用:

accounts.foo: Accessor for m2m field 'bar' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'bar'.
accounts.foo: Reverse query name for m2m field 'bar' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'bar'.
accounts.foo: Accessor for m2m field 'baz' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'baz'.
accounts.foo: Reverse query name for m2m field 'baz' clashes with related m2m field 'Child.+'. Add a related_name argument to the definition for 'baz'.

我需要做些什么来避免产生反向关系？

Answer 1

我想你需要给两个字段不同的related_names:

class Child(models.Model):
  name = models.CharField(max_length=80)

class Foo(models.Model):
  bar = models.ManyToManyField(Child, related_name="bar")
  baz = models.ManyToManyField(Child, related_name="baz")

如果您没有提供相关名称,那么它会尝试foo_set在Child模型上创建两次相同的访问者名称().如果您提供相同的相关名称,它将再次尝试创建两次相同的访问者,因此您需要提供唯一的相关名称.使用上面的代码来定义模型,然后给定一个Child实例c,您可以Foo使用c.bar.all()和访问相关对象c.baz.all().

如果您不想要向后关系,则将a附加+到每个(唯一的)相关名称:

class Foo(models.Model):
  bar = models.ManyToManyField(Child, related_name="bar+")
  baz = models.ManyToManyField(Child, related_name="baz+")

Answer 2

你还没有仔细阅读Django的文档.这里说:

如果您有多个指向同一模型的ManyToManyField并且想要抑制向后关系,请将每个related_name设置为以"+"结尾的唯一值.

该related_name属性必须是唯一的,不一样的.