在Django使用F()和timedelta进行查询 [英] Making queries using F() and timedelta at django

问题描述

我有以下模型:

class Process(models.Model):
  title = models.Charfield(max_length=255)
  date_up = models.DateTimeField(auto_now_add=True)
  days_activation = models.PositiveSmallIntegerField(default=0)

现在，我需要根据其days_activation的值来查询所有已过期的Process对象.

Now I need to query for all Process objects that have expired, according to their value of days_activation.

我尝试过

from datetime import datetime, timedelta

Process.objects.filter(date_up__lte=datetime.now()-timedelta(days=F('days_activation')))

并收到以下错误消息:

TypeError:timedelta days组件的不受支持的类型:F

我当然可以用Python做到:

I can of course do it in Python:

filter (lambda x: x.date_up<=datetime.now() - timedelta(days=x.days_activation), 
        Process.objects.all ()), 

但是我真的需要产生一个django.db.models.query.QuerySet.

but I really need to produce a django.db.models.query.QuerySet.

推荐答案

您必须扩展Aggregate.像下面这样:

You have to extend Aggregate. Do like below:

from django.db import models as DM

class BaseSQL(object):
    function = 'DATE_SUB'
    template = '%(function)s(NOW(), interval %(expressions)s day)'

class DurationAgr(BaseSQL, DM.Aggregate):
    def __init__(self, expression, **extra):
        super(DurationAgr, self).__init__(
            expression,
            output_field=DM.DateTimeField(),
            **extra
        )

Process.objects.filter(date_up__lte=DurationAgr('days_activation'))

希望它会为您工作. :)

Hopefully, It will work for you. :)

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