问题
I'm trying to do some complex ordering based on promotions: an article is promoted every 7th day since creation (the articles expire after 30 days).
My approach is to annotate the queryset with the number of days since it was created, but the value of the annotated field (days_since_creation
), in my code, is always 0.
from datetime import timedelta
from django.test import TestCase
from django.db.models import ExpressionWrapper, F
from django.db.models.fields import IntegerField
from django.utils import timezone
from .models import Article
# class Article(models.Model):
# title = models.CharField(max_length=150)
# creation_date = models.DateTimeField()
#
# def __str__(self):
# return self.title
class ArticleTestCase(TestCase):
def test_days_since_creation(self):
now = timezone.now()
objects_data = [
Article(
title='Alrp',
creation_date=(now - timedelta(days=5)) # 5 days ago
),
Article(
title='Bopp',
creation_date=(now - timedelta(days=7)) # 7 days ago
),
Article(
title='Crkp',
creation_date=(now - timedelta(days=14)) # 14 days ago
),
]
Article.objects.bulk_create(objects_data)
article_set = Article.objects\
.annotate(
days_since_creation=ExpressionWrapper(
now - F('creation_date'),
output_field=IntegerField()
)
)
for article in article_set:
print(article.days_since_creation)
# all 3 objects print "0"
I expected the value for each object to be 5, 7, 14 repectively. I even tried DurationField
but that just printed 0:00:00.
After that I would annotate the queryset again with an order
field that has the value 0 if the value of days_since_past
is in [0, 7, 14, 21, 28,]
or 1 otherwise, and then order_by('order')
.
回答1:
It's a little bit hacky, but works. You need to convert now
to DateTimeField
. Result will be in DurationField
- standard for timedelta. For order
we are going to use Case
to check whether or not we are in selected duration and then we sort it.
I specifically change initial order of Articles
to test ordering.
from datetime import timedelta
from django.test import TestCase
from django.db.models import ExpressionWrapper, F, Value, Case, When
from django.db.models.fields import DateTimeField, DurationField, BooleanField
from django.utils import timezone
from .models import Article
class ArticleTestCase(TestCase):
def test_days_since_creation(self):
now = timezone.now()
order_in_variants = [
timedelta(days=0),
timedelta(days=7),
timedelta(days=14),
timedelta(days=21),
timedelta(days=28),
]
objects_data = [
Article(
title='Crkp',
creation_date=(now - timedelta(days=14)) # 14 days ago
),
Article(
title='Alrp',
creation_date=(now - timedelta(days=5)) # 5 days ago
),
Article(
title='Bopp',
creation_date=(now - timedelta(days=7)) # 7 days ago
),
]
Article.objects.bulk_create(objects_data)
article_set = Article.objects.all().annotate(
days_since_creation=ExpressionWrapper(
Value(now, DateTimeField()) - F('creation_date'),
output_field=DurationField()
)
).annotate(
order=Case(
When(days_since_creation__in=order_in_variants, then=Value(False)),
default=Value(True),
output_field=BooleanField(),
)
).order_by('order')
for article in article_set:
print(article.days_since_creation.days, article.order)
# 14 False
# 7 False
# 5 True
You also might want to check that days_since_creation
in range instead of being exactly 7 days difference. Makes it even uglier, but still:
order_in_variants = [
(timedelta(days=0), timedelta(days=0, hours=23, minutes=59, seconds=59, microseconds=999999)),
(timedelta(days=7), timedelta(days=7, hours=23, minutes=59, seconds=59, microseconds=999999)),
(timedelta(days=14), timedelta(days=14, hours=23, minutes=59, seconds=59, microseconds=999999)),
(timedelta(days=21), timedelta(days=21, hours=23, minutes=59, seconds=59, microseconds=999999)),
(timedelta(days=28), timedelta(days=28, hours=23, minutes=59, seconds=59, microseconds=999999)),
]
# ...
order=Case(
When(days_since_creation__range=order_in_variants[0], then=Value(False)),
When(days_since_creation__range=order_in_variants[1], then=Value(False)),
When(days_since_creation__range=order_in_variants[2], then=Value(False)),
When(days_since_creation__range=order_in_variants[3], then=Value(False)),
When(days_since_creation__range=order_in_variants[4], then=Value(False)),
default=Value(True),
output_field=BooleanField(),
)
来源:https://stackoverflow.com/questions/55998706/how-to-annotate-a-queryset-with-number-of-days-since-creation