Django按月注释分组

Question

我有一个非常基本的模型：

class Link(models.Model):
    title = models.CharField(max_length=250, null=False)
    user = models.ForeignKey(User)
    url = models.CharField(max_length=250, blank=True, null=True)
    link_count = models.IntegerField(default=0)
    pub_date = models.DateField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)

我可以使用以下命令创建按日期分组的所有条目的列表：

Link.objects.values('pub_date').order_by('-pub_date').annotate(dcount=Count('pub_date'))

这自然会按天对项目进行分组。但我真正想做的是按月分组。我是否可以使用annotate（）完成此操作？

非常感谢

克

Answer 1

如果您使用的是PostgreSQL，则以下操作可能有效：

from django.db.models import Count

Link.objects.extra(select={'month': 'extract( month from pub_date )'}).values('month').annotate(dcount=Count('pub_date'))

我不确定extract在其他数据库中的可移植性如何。

Answer 2

要添加，作为使用extra()的替代方法：自Django 1.8以来，还可以使用条件表达式。

>>> year_overview = Link.objects.filter(pub_date__year=year).aggregate(
    jan=Sum(
        Case(When(created__month=0, then=1),
             output_field=IntegerField())
    ),
    feb=Sum(
        Case(When(created__month=1, then=1),
             output_field=IntegerField())
    ),
    mar=Sum(
        Case(When(created__month=2, then=1),
             output_field=IntegerField())
    ),
    apr=Sum(
        Case(When(created__month=3, then=1),
             output_field=IntegerField())
    ),
    may=Sum(
        Case(When(created__month=4, then=1),
             output_field=IntegerField())
    ),
    jun=Sum(
        Case(When(created__month=5, then=1),
             output_field=IntegerField())
    ),
    jul=Sum(
        Case(When(created__month=6, then=1),
             output_field=IntegerField())
    ),
    aug=Sum(
        Case(When(created__month=7, then=1),
             output_field=IntegerField())
    ),
    sep=Sum(
        Case(When(created__month=8, then=1),
             output_field=IntegerField())
    ),
    oct=Sum(
        Case(When(created__month=9, then=1),
             output_field=IntegerField())
    ),
    nov=Sum(
        Case(When(created__month=10, then=1),
             output_field=IntegerField())
    ),
    dec=Sum(
        Case(When(created__month=11, then=1),
             output_field=IntegerField())
    ),
)

>>> year_overview
{'mar': None, 'feb': None, 'aug': None, 'sep': 95, 'apr': 1, 'jun': None, 'jul': None, 'jan': None, 'may': None, 'nov': 87, 'dec': 94, 'oct': 100}

Answer 3

from django.db import connections
from django.db.models import Count

Link.objects.extra(select={'month': connections[Link.objects.db].ops.date_trunc_sql('month', 'pub_date')}).values('month').annotate(dcount=Count('pub_date'))