问题描述
Django 1.7 的文档提到了RunSQL
类可用于在表上创建部分索引.我有一个表格,我想要 title
、blog
和 & 的组合.category
是唯一的.但是,如果未提供类别,则 title 和博客应该仍然是独一无二的.
The documentation for Django 1.7 mentions RunSQL
classes can be used to create partial indexes on your tables. I have a table where I want the combination of title
, blog
& category
to be unique. However if category is not provided, the combination of title & blog should still be unique.
class Post(models.Model):
title = models.CharField(max_length=200)
blog = models.ForeignKey(Blog)
category = models.ForeignKey(Category, null=True, blank=True)
我可以通过部分索引来实现这个约束(就像下面显示的 SQL).如果我使用的是 Django 1.7 迁移,我应该在哪里添加此代码?
I can achieve this constraint with partial indexes (like the SQL shown below). Where do I add this code if I'm using Django 1.7 migrations?
CREATE UNIQUE INDEX idx1
ON Post (title, blog_id, category_id)
WHERE category_id IS NOT NULL;
CREATE UNIQUE INDEX idx2
ON Post (title, blog_id)
WHERE category_id IS NULL;
推荐答案
Django 2.2 及更高版本
从 2.2 版开始,Django 支持声明性部分唯一索引 支持它们的数据库(PostgreSQL 和 SQLite).所以你可以这样做:
As of version 2.2 Django supports declarative partial unique indexes on databases that support them (PostgreSQL and SQLite). So you could do something like:
from django.db.models import Model, Q, UniqueConstraint
class Post(Model):
...
class Meta:
constraints = [
UniqueConstraint(
fields=["title", "blog", "category"],
name="idx1",
condition=Q(category__isnull=False)),
UniqueConstraint(
fields=["title", "blog"],
name="idx2",
condition=Q(category__isnull=True)),
]
Django 2.1 及更早版本
在旧版本中,您需要通过迁移来执行此操作.首先创建一个新的空迁移文件:
In older versions you need to do this with migrations. First create a new, empty migration file:
python manage.py makemigrations --empty yourappname
然后,为每个索引添加适当的 RunSQL
行:
Then, for each index add an appropriate RunSQL
line:
operations = [
migrations.RunSQL("CREATE UNIQUE INDEX..."),
migrations.RunSQL("CREATE UNIQUE INDEX..."),
]
最后,运行migrate
.
这篇关于使用 Django 1.7 创建部分索引的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!