Django queryset中的模数? [英] Modulo in django queryset?

问题描述

是否已经有一种方法可以根据Django queryset中的 id％4 == 0 选择对象?

Is there already a way to select objects according to id % 4 == 0 in django queryset ?

到目前为止，我发现的唯一解决方案是编写自定义Transform，因为Postgresql中似乎支持模数，但出现错误.

The only solution I found so far is to write a custom Transform since modulo seems to be supported in Postgresql but I got errors.

这是我的代码:

from django.db.models import Lookup, Transform
from django.db.models.fields import Field, IntegerField, AutoField

class Modulo4(Transform):
    lookup_name = 'modulo4'

    def as_sql(self, compiler, connection):
        lhs, params = compiler.compile(self.lhs)
        return "%s %% 4" % lhs, params

AutoField.register_lookup(Modulo4)

foos = Foo.filter(id__modulo4=0)

当评估查询集时(使用 foos.count()或其他方法)时出现错误:

And I get an error when the queryset is evaluated (with foos.count() or whatever):

IndexError: tuple index out of range

指的是Django文件.这似乎是由于模，因为我设法使用

refering to a django file. It seems to be due to the modulo since I manage to make the custom transform work with the doc example.

关于如何实现此目标的任何想法?

Any idea on how to achieve this ?

推荐答案

我手头没有Django 1.8进行测试，但是看起来您可以使用

I don't have Django 1.8 at hand to test it, but looks like you can do this using F with annotation, like this:

Foo.objects.annotate(idmod4=F('id') % 4).filter(idmod4=0)

(Django 1.7和更早版本不支持在 annotate 中使用F)

(Django 1.7 and earlier doesn't support using F in annotate)

对于Django 1.7和更早版本，您始终可以使用 .extra() ，但不是很漂亮:

For Django 1.7 and earlier you can always use .extra() but it isn't very pretty:

Foo.objects.extra(where=["id %% %s = 0"], params=[4])

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