Django在BooleanField上注释 [英] Django annotate on BooleanField

问题描述

我有以下模型：

class Foo(models.Model):
    pass

class Bar(models.Model):
    foo = models.ForeignKey(Foo)
    is_successful = models.BooleanField()

我想获取所有 foo 对象，如果所有 bar <与 foo 对象关联的/ code>对象的 is_successful 为 True

I would like to get all foo objects with an annotation if all of the bar objects associated with foo object have is_successful as True

到目前为止，我的查询集是：

So far my queryset is:

foos = Foo.objects.all().annotate(all_successful=Min('bar__is_successful'))

The all_successful 批注的想法是，如果所有 is_successful 行的最小值为1，则所有行必须为 True （假设 0 是 False 和 1 是 True ）。所以知道我可以这样使用查询集：

The idea for the all_successful annotation is that if the minimum value of all is_successful rows is 1, then all of them must be True (assuming 0 is False and 1 is True). So knowing that I can use the queryset like so:

foo = foos[0]

if foo.all_successful == 1:
    print 'All bars are successful'
else:
    print 'Not all bars are successful'

这在sqlite中效果很好，但在PostgreSQL中失败，因为PostgreSQL无法在布尔列上执行 MIN 聚合。我猜这在sqlite中行得通，因为sqlite将布尔值视为整数，因此它可以执行聚合。

This works great in sqlite however it fails in PostgreSQL because PostgreSQL can't execute MIN aggregate on a boolean column. I guess this works in sqlite because sqlite treats bools as integers hence it can execute the aggregate.

我的问题是如何在不转换是否成功字段到 IntegerField ？

My question is how can I make this queryset work in PostgreSQL without converting my is_successful field to an IntegerField?

感谢

推荐答案

我知道这是一个老问题，但是最近我遇到了这个问题。 Django v1.8现在已经内置了对case / when的支持，因此您可以使用ORM而不是使用自定义SQL进行修改。

I know this is an old question, but I ran up against this recently. Django v1.8 now has built in support for case/when, so you can use the ORM instead of hacking around with custom SQL.

https://docs.djangoproject.com/zh-CN/1.8/ref/models/conditional-表达式/＃case

Foo.objects.annotate(
    all_successful=Case(
        When(bar__is_successful=False, then=False),
        When(bar__is_successful=True, then=True),
        default=False,
        output_field=BooleanField()
    ))

我还没有尝试过，但是在最近的一个项目中，类似的东西对我有用。

I haven't tried this out, but something similar worked for me on a recent project.

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