I'd like to filter that implements this "pseudocode":
Post.objects.filter(Post.timestamp + Post.duration > datetime.datetime.now())
I also would like to wrap this in a Django management command.
Any help would be great!
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You need to research how to write filter queries first; that's not valid Django at all.Daniel Roseman– Daniel Roseman2016-02-26 18:09:23 +00:00Commented Feb 26, 2016 at 18:09
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I tried to solve this problem on my on. I found this documantation: docs.djangoproject.com/en/1.9/howto/custom-management-commands I found a few errors I made but no solution to my problem.I would really appreciate help!Kaesekante– Kaesekante2016-02-26 20:01:06 +00:00Commented Feb 26, 2016 at 20:01
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1 Answer
Filter
Not sure how your fields look but here's a hint:
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()
)
)
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/en/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
Management Command
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()
More details: https://docs.djangoproject.com/en/1.9/howto/custom-management-commands/
2 Comments
Kaesekante
Can you give me a hint for the filter? The basic idea was, that timestamp is the creationdate and the user can pick how long the post should last. The timestamp comes from a DateTimeField and duration from a tupel of Durationfield.
bakkal
I posted some hints, to annotate the value with an F expression and then filtering by it, that should do it. If you run into issues please post your model fields and I'll make actual code for it tomorrow!