python - 如何在 Django 中使用表达式进行过滤

Question

我想要实现这个“伪代码”的过滤器:

   Post.objects.filter(Post.timestamp + Post.duration > datetime.datetime.now())

我还想将其包装在 Django 管理命令中。

任何帮助都会很棒!

Answer 1

过滤器

不确定您的字段看起来如何，但这里有一个提示:

让我们组成一个 F 表达式，像这样 F('timestamp') - F('duration')，并用它注释我们的查询:

from django.db.models import DateTimeField, ExpressionWrapper, F

Post.objects.annotate(
        timestamp_minus_duration=ExpressionWrapper(
            F('timestamp') + F('duration'),
            output_field=DateTimeField()
        )
    )

现在您可以使用带注释的字段进行过滤

   Post.objects.annotate(
        timestamp_minus_duration=ExpressionWrapper(
            F('timestamp') + F('duration'),
            output_field=DateTimeField()
        )
    ).filter(
        timestamp_minus_duration__gt=datetime.datetime.now()
    )

引用:https://docs.djangoproject.com/en/1.9/topics/db/queries/#using-f-expressions-in-filters

引用:https://docs.djangoproject.com/es/1.9/ref/models/expressions/#using-f-with-annotations

引用:https://docs.djangoproject.com/es/1.9/topics/db/aggregation/#filtering-on-annotations

管理命令

将代码放在命令的handle()方法中即可

# yourapp/management/commands/deletepost.py

from django.core.management.base import BaseCommand, CommandError
from yourapp.models import Post

class Command(BaseCommand):
    help = 'Describe your cmd here'

    def handle(self, *args, **options):
           Post.objects.annotate(...).filter(...).delete()

更多详情:https://docs.djangoproject.com/en/1.9/howto/custom-management-commands/