具有未继承约束的 Django 模型抽象模型：'constraints' 指的是字段 'xxx'，它不是模型 'Foo' 的本地字段

Question

我正在使用 Django 3.2

我遇到了一个似乎是错误的奇怪行为； ABC 中定义的约束中使用的字段不会被子类.

继承

myapp/models.py

class BaseFoo(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE,related_name='%(class)s_content_type')
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')
    user = models.ForeignKey(User, blank=False, null=False, on_delete=models.CASCADE,related_name='%(class)s')
    created = models.DateTimeField(auto_now_add=True)

    class Meta:
        abstract = True
        constraints = [
            models.UniqueConstraint(fields=['content_object', 'user'], name="'%(class)s_unique"),
        ]
    
class Foo(BaseFoo):
    class Meta(BaseFoo.Meta):
        abstract = False

当我 makemigrations 时没问题，但是，当我尝试迁移架构时（`python manage.py 迁移），我收到以下错误：

myapp.Foo: (models.E016) 'constraints' refers to field 'content_object' which is not local to model 'Foo'. HINT: This issue may be caused by multi-table inheritance.

为什么Foo没有继承父类ABC明确定义的字段？ - 我该如何解决这个问题（假设这不是错误）？

Answer 1

1. 不能使用 GenericForeignKey in UniqueConstraint, because a GenericForeignKey 不是普通的字段对象。而在 UniqueConstraint 中使用 content_type 和 object_id，这等同于 content_object：


class Meta:
    abstract = True
    constraints = [
        models.UniqueConstraint(
            <b>fields=['content_type', 'object_id', 'user']</b>, 
            <b>name="%(app_label)s_%(class)s_user_unique")</b>,
    ]

参见Django Docs：

Due to the way GenericForeignKey is implemented, you cannot use such fields directly with filters (filter() and exclude(), for example) via the database API. Because a GenericForeignKey isn’t a normal field object.

Likewise, GenericForeignKey does not appear in ModelForms.

2. 根据Django Docs in abstract base classes related_name必须包含'%(app_label)s' 和 '%(class)s'。并且您应该始终为字段指定唯一的反向名称和查询名称。

content_type = models.ForeignKey(
   ContentType, on_delete=models.CASCADE,
   related_name='<b>%(app_label)s_%(class)s</b>_content_types',
   <b>related_query_name='%(app_label)s_%(class)s_content_type'</b>,
)

user = models.ForeignKey(
    User, blank=False, null=False,
    on_delete=models.CASCADE,
    related_name='<b>%(app_label)s_%(class)s</b>_users',
    related_query_name='%(app_label)s_%(class)s_user',
)

If you are using related_name or related_query_name on a ForeignKey or ManyToManyField, you must always specify a unique reverse name and query name for the field. This would normally cause a problem in abstract base classes, since the fields on this class are included into each of the child classes, with exactly the same values for the attributes (including related_name and related_query_name) each time.

To work around this problem, when you are using related_name or related_query_name in an abstract base class (only), part of the value should contain '%(app_label)s' and '%(class)s'.

具有未继承约束的 Django 模型抽象模型：'constraints' 指的是字段 'xxx'，它不是模型 'Foo' 的本地字段

Django model abstract model with constrains not being inherited: 'constraints' refers to field 'xxx' which is not local to model 'Foo'

django

django-models

django-orm

django-migrations

myapp/models.py