我如何设置一个表约束为“可延迟的初始延迟”？在Django模型中？

问题描述

我正在尝试使用PostgreSQL数据库为django中的表模型设置约束。

I am trying to set a constraint to a table model in django with a postgresql database.

我可以使用以下语句通过postgresql做到这一点：

I can do it via postgresql with this sentence:

ALTER TABLE public.mytable ADD CONSTRAINT "myconstraint" UNIQUE(field1, field2) DEFERRABLE INITIALLY DEFERRED;

但是我想通过Django模型实现。
阅读django官方文档时，我没有发现任何相关内容。

But I want to do it via django model.Reading the django official documentation I have not found anything related.

我需要这样的东西：

class Meta:
  unique_together = (('field1', 'field2',), DEFERRABLE INITIALLY DEFERRED)

是否可以做这样的事情？

Is it possible to do something like this?

推荐答案

Django

您可以使用自定义SQL来实现。在您的 models.py 中，添加以下内容：

You can do it with custom SQL. In your models.py, add this:

from django.db import connection
from django.db.models.signals import post_migrate

def after_migrate(sender, **kwargs):
    cursor = connection.cursor()
    cursor.execute('ALTER TABLE public.mytable ALTER CONSTRAINT '
                   'myconstraint DEFERRABLE INITIALLY DEFERRED')

post_migrate.connect(after_migrate)

尽管我过去做过这样的事情，但我发现多年来，我宁愿保持工作简单，独立于任何特定的RDBMS。例如，您确实要支持SQLite，因为它使开发变得如此容易。在设计上稍作更改，您通常可以摆脱这些东西。

Although I've done such things in the past, I've found that over the years I prefer to keep my work simpler and independent from any specific RDBMS. For example, you really want to support SQLite, because it makes development so much easier. With a little change in design you can often get rid of such stuff.

更新：我认为@fpghost的答案更好。我不知道我在想什么：-）

Update: I think @fpghost's answer is better. I don't know what I was thinking :-)

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