如何在Django中使用表达式进行过滤 [英] How to filter using an expression in Django
问题描述
我想过滤器来实现此伪代码":
I'd like to filter that implements this "pseudocode":
Post.objects.filter(Post.timestamp + Post.duration > datetime.datetime.now())
我也想将其包装在Django管理命令中.
I also would like to wrap this in a Django management command.
任何帮助都会很棒!
推荐答案
过滤器
不确定字段的外观,但这是一个提示:
Filter
Not sure how your fields look but here's a hint:
让我们像这样的F('timestamp') - F('duration')
组成一个 F表达式,并用它来注释我们的查询:
Let's compose an F expression like this F('timestamp') - F('duration')
, and annotate our query with it:
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
Now you can filter with that annotated field
Post.objects.annotate(
timestamp_minus_duration=ExpressionWrapper(
F('timestamp') + F('duration'),
output_field=DateTimeField()
)
).filter(
timestamp_minus_duration__gt=datetime.datetime.now()
)
ref: https://docs.djangoproject.com/zh-CN/1.9/topics/db/queries/#using-f-expressions-in-filters
ref: https://docs.djangoproject.com/es/1.9/ref/models/expressions/#using-f-with-annotations
ref: https://docs. djangoproject.com/es/1.9/topics/db/aggregation/#filtering-on-annotations
只需将代码放入命令的handle()
方法中
Just put the code in the handle()
method of the command
# 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()
更多详细信息: https://docs.djangoproject.com/en/1.9/howto/custom-management-commands/
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