Question

我正在尝试基于促销进行一些复杂的排序：自创建以来，文章每隔7天就会进行一次推广（文章在30天后失效）。

我的方法是用自创建以来的天数对查询集进行注释，但是在我的代码中，带注释的字段（days_since_creation）的值始终为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"

我希望每个对象的值分别为5、7、14。我什至尝试了DurationField，但只打印了0:00:00。

此后，如果order的值位于days_since_past中，则我将再次使用[0, 7, 14, 21, 28,]字段注释该查询集，该字段的值为0，否则为1，然后为{{1} }。

Answer 1

有点黑，但是可以用。您需要将now转换为DateTimeField。结果将以DurationField-timedelta的标准格式。对于order，我们将使用Case来检查是否在选定的持续时间内，然后对其进行排序。

我专门更改了Articles的初始顺序以测试顺序。

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

您可能还想检查范围内的days_since_creation，而不是恰好相差7天。使它更加难看，但仍然：

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(),
            )

如何用自创建以来的天数注释查询集

1 个答案: