Django抽象模型中能否声明两个指向同表的ForeignKey？

你想在抽象模型TrackableDateModel中同时添加create_user和update_user两个指向User表的ForeignKey，但添加update_user后执行makemigrations时出现反向访问器冲突报错：

ERRORS:
DjModule.A.create_user: (fields.E304) Reverse accessor 'User.create_user' for 'DjModule.A.create_user' clashes with reverse accessor for DjModule.B.create_user'.
HINT: Add or change a related_name argument to the definition for 'DjModule.A.Export4Payment.create_user' or 'DjModule.B.create_user'.

原代码如下：

class TrackableDateModel(models.Model):
    """Abstract model to Track the creation/updated date for a model."""
    create_date = models.DateTimeField(auto_now_add=True, help_text="Creation time", verbose_name="Created", null=True, blank=True)
    create_user = models.ForeignKey(User, related_name="create_user", on_delete=models.CASCADE, help_text="Who created", verbose_name="Author", null=True, blank=True)
    update_date = models.DateTimeField(auto_now=True, help_text="Time of change", verbose_name="Changed", null=True, blank=True)

    class Meta:
        abstract = True


class A(TrackableDateModel):
    ....

class B(TrackableDateModel):
    .....

尝试添加的字段：

update_user = models.ForeignKey(User, related_name="update_user", on_delete=models.CASCADE, help_text="Who modified", verbose_name="Author of change", null=True, blank=True)

错误原因 #

所有继承该抽象模型的子类（比如A、B）会共享相同的related_name值，导致User模型上生成的反向访问器名称重复，引发冲突。

解决办法 #

使用Django提供的%(class)s占位符，让每个子类的related_name自动带上自身类名，避免重复。修改后的抽象模型代码如下：

from django.contrib.auth.models import User
from django.db import models

class TrackableDateModel(models.Model):
    """Abstract model to Track the creation/updated date for a model."""
    create_date = models.DateTimeField(auto_now_add=True, help_text="Creation time", verbose_name="Created", null=True, blank=True)
    create_user = models.ForeignKey(
        User, 
        related_name="created_%(class)s", 
        on_delete=models.CASCADE, 
        help_text="Who created", 
        verbose_name="Author", 
        null=True, 
        blank=True
    )
    update_date = models.DateTimeField(auto_now=True, help_text="Time of change", verbose_name="Changed", null=True, blank=True)
    update_user = models.ForeignKey(
        User, 
        related_name="updated_%(class)s", 
        on_delete=models.CASCADE, 
        help_text="Who modified", 
        verbose_name="Author of change", 
        null=True, 
        blank=True
    )

    class Meta:
        abstract = True


class A(TrackableDateModel):
    # 子类自定义字段
    pass

class B(TrackableDateModel):
    # 子类自定义字段
    pass

效果说明 #

• 对于A类，create_user对应的反向访问器变为User.created_a.all()，update_user对应的反向访问器变为User.updated_a.all()
• 对于B类，反向访问器则是User.created_b.all()和User.updated_b.all()
• 这样就不会出现反向访问器名称冲突的问题，执行makemigrations和migrate都能正常完成

内容的提问来源于stack exchange，提问作者Victor