Question

我有以下用django编写的代码

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

class AuditColumns(models.Model):
    created_at=models.DateField("Created at")
    created_by=models.ForeignKey(User, db_column="created_by", related_name="poll_user_created_by")
    updated_at=models.DateTimeField("Updated at")
    updated_by=models.ForeignKey(User, db_column="updated_by", null=True, related_name="poll_user_updated_by")
    class Meta:
        abstract = True


class Poll(AuditColumns):
    question=models.CharField(max_length=300)
    start_poll_at=models.DateTimeField(null=True)
    end_poll_at=models.DateTimeField(null=True)
    is_active=models.BooleanField(default=True)


class Choice(AuditColumns):
    choice=models.CharField(max_length=200)

当我执行此代码时出现以下错误

mo@debian:~/PycharmProjects/KlamTam$ ./manage.py sql polls
Error: One or more models did not validate:
polls.poll: Accessor for field 'created_by' clashes with related field 'User.poll_user_created_by'. Add a related_name argument to the definition for 'created_by'.
polls.poll: Reverse query name for field 'created_by' clashes with related field 'User.poll_user_created_by'. Add a related_name argument to the definition for 'created_by'.
polls.poll: Accessor for field 'updated_by' clashes with related field 'User.poll_user_updated_by'. Add a related_name argument to the definition for 'updated_by'.
polls.poll: Reverse query name for field 'updated_by' clashes with related field 'User.poll_user_updated_by'. Add a related_name argument to the definition for 'updated_by'.
polls.choice: Accessor for field 'created_by' clashes with related field 'User.poll_user_created_by'. Add a related_name argument to the definition for 'created_by'.
polls.choice: Reverse query name for field 'created_by' clashes with related field 'User.poll_user_created_by'. Add a related_name argument to the definition for 'created_by'.
polls.choice: Accessor for field 'updated_by' clashes with related field 'User.poll_user_updated_by'. Add a related_name argument to the definition for 'updated_by'.
polls.choice: Reverse query name for field 'updated_by' clashes with related field 'User.poll_user_updated_by'. Add a related_name argument to the definition for 'updated_by'.

这与设置唯一的related_name有关，有没有办法动态生成related_names以确保它们始终是唯一的？当然最好知道什么是related_name，如果可能的话，避免设置它们？

此致

Answer 1

Django ORM提供了相关名称，使您可以轻松找到键入当前模型的所有模型。因此，如果您有一个从Foo到Bar的键，默认情况下，Bar的实例将具有一个名为foo_set的属性，该属性将为您提供链接到该特定Bar的所有Foo的列表。

您可以使用更自然/适当的related_names指定您自己的相关名称，以便更容易回读代码。

然而，正如您所看到的，Django的ORM需要唯一的related_name值，并且因为您的基类中有FK，它会自动为所有子模型创建这些FK并使用相同的名称，这显然是 - - 不可行。

好消息是，this note in the documentation shows a workaround for Django 1.2+

如果由于某种原因，你不得不使用Django 1.1或更早版本，这里有一个替代的解决方法：不使用抽象模型上的FK，只需使用一个字段来存储键控模型的pk，并添加访问器因此。例如：

class AuditBase(models.Model):
    created_at = models.DateTimeField("Created at", auto_now_add=True)
    created_by = models.IntegerField(required=True)
    updated_at = models.DateTimeField("Updated at", auto_now=True)
    updated_by = models.IntegerField(required=True)

    class Meta:
        abstract = True

@property
def creator(self):
    return User.objects.get(id=self.created_by) 

@property
def last_editor(self):
    return User.objects.get(id=self.updated_by)

def save(self, *args, **kwargs):
    #track the creator/last editor via an optional kwarg
    active_user = self.kwargs.get('user')
    if active_user:
       self.updated_by = active_user
    if active_user and not self.created_by:
       self.created_by = active_user

    return super(AuditBase, self).save(*args, **kwargs)

使用外键继承抽象类时出错

1 个答案: