Django

Question

所以我有一个用户 class 并且一个用户可以关注另一个用户，但我不希望用户能够关注他们自己。有没有办法将此约束添加到 Django？

class FollowUser(AbstractSimpleModel):
    follower_id = models.ForeignKey(User, on_delete=models.CASCADE, related_name='follower_id')
    followee_id = models.OneToOneField(User, on_delete=models.CASCADE, related_name='followee_id')

Answer 1

由于您需要根据其他字段的值来验证该字段的值，这里是 FollowUser.follower_id 和 FollowUser.followee_id，您可以遵循 Django 如何处理 validation of fields 的过程：

在您要运行验证的地方实施Model.clean()
覆盖 Model.save() 以通过 Model.full_clean() 调用完整的验证过程。需要这个明确的步骤，因为如文件所示：

Note that full_clean() will not be called automatically when you call your model’s save() method. You’ll need to call it manually when you want to run one-step model validation for your own manually created models. For example:

from django.core.exceptions import ValidationError
from django.db import models


class UserDummy(models.Model):
    pass

class FollowUser(models.Model):
    follower_id = models.ForeignKey(UserDummy, on_delete=models.CASCADE, related_name='follower_id')
    followee_id = models.OneToOneField(UserDummy, on_delete=models.CASCADE, related_name='followee_id')

    def clean(self):
        if self.follower_id == self.followee_id:
            raise ValidationError("Users can't follow themselves")

    def save(self, *args, **kwargs):
        self.full_clean()
        super().save(*args, **kwargs)

样本运行

设置数据：

>>> from my_app.models import *
>>> UserDummy.objects.values()
<QuerySet [{'id': 1}, {'id': 2}, {'id': 3}]>
>>> user1 = UserDummy.objects.get(id=1)
>>> user2 = UserDummy.objects.get(id=2)
>>> user3 = UserDummy.objects.get(id=3)

验证失败：

>>> # Using Model.save()
>>> FollowUser(follower_id=user1, followee_id=user1).save()
Traceback (most recent call last):
    raise ValidationError(errors)
django.core.exceptions.ValidationError: {'__all__': ["Users can't follow themselves"]}
>>> 
>>> # Using Model.objects.create()
>>> FollowUser.objects.create(follower_id=user1, followee_id=user1)
Traceback (most recent call last):
    raise ValidationError(errors)
django.core.exceptions.ValidationError: {'__all__': ["Users can't follow themselves"]}

验证成功：

>>> # Using Model.save()
>>> FollowUser(follower_id=user1, followee_id=user2).save()
>>> 
>>> # Using Model.objects.create()
>>> FollowUser.objects.create(follower_id=user2, followee_id=user3)
<FollowUser: FollowUser object (2)>
>>> 
>>> FollowUser.objects.values()
<QuerySet [{'id': 1, 'follower_id_id': 1, 'followee_id_id': 2}, {'id': 2, 'follower_id_id': 2, 'followee_id_id': 3}]>

注意：请注意，如果您使用 Model.objects.bulk_create()，您将需要进一步更改，因为它不会调用记录的 Model.save() 功能：

bulk_create()

The model’s save() method will not be called, and the pre_save and post_save signals will not be sent.

Django - 确保同一模型类型的 table 中的 2 个字段对实体没有相同的值

Django - Ensure 2 fields in a table of the same model type don't have the same value for an entity

python

relational-database

样本运行