mysql - 如何在 Django 中将外键表示为一对？

Question

以下是一些 Django 模型:

class User (Model):
    name = CharField (max_length=100)

class ThingVersion (Model):
    timestamp = DateTimeField (auto_now_add = True)

class ThingPartition (Model):
    version          = ForeignKey (ThingVersion)
    partition_number = IntegerField ()

class UserInPartition (Model):
    user             = ForeignKey (User)
    version          = ForeignKey (ThingVersion)
    partition_number = IntegerField ()

    class Meta:
        unique_together = (('user', 'version'))

我故意不做“显而易见”的事情，就是这个

class UserInPartition (Model):
    user      = ForeignKey (User)
    partition = ForeignKey (ThingPartition)

因为我需要 unique_together 约束，据我所知，如果我使用更规范化的 partition =foreignKey (ThingPartition) 方法，则无法表达该约束。

如何表达 UserInPartition.(version,partition_number) 对是 ThingPartition 的外键？

Alternatively, is there a way to use the normalized partition = ForeignKey (ThingPartition) approach and constrain the UserInPartition model to only have one partition_number per (user,version)?

Answer 1

我正在尝试了解您想要实现的目标，以便提供更好的答案。为什么分区和事物分区中的用户都有分区号？

但是您可以做的是将 ThingPartition 转换为多对多关系的 Through 模型。

https://docs.djangoproject.com/en/2.0/ref/models/fields/#django.db.models.ManyToManyField.through

基本上使用 through 模型将完全满足您的要求 -

• 有一个模型，其中引用分区中的用户、分区号和版本
• 对该模型中的所有 3 件事强制执行唯一性

基本上，您的设置如下所示:

class User (Model):
    name = CharField (max_length=100)
    something_that_makes_sense = ManyToManyField(ThingVersion, through=ThingPartition)

class ThingVersion (Model):
    timestamp = DateTimeField (auto_now_add = True)

class ThingPartition (Model):
    user             = ForeignKey (User)
    version          = ForeignKey (ThingVersion)
    partition_number = IntegerField ()

    class Meta:
        unique_together = ('user', 'version', 'partition_number')

根据我有限的知识，这将是我最好的报价。