Django 模型组按日期时间的日期 [英] Django model group by datetime's date

问题描述

假设我有一个这样的模型:

Assume I have a such model:

class Entity(models.Model):
    start_time = models.DateTimeField()

我想将它们重新组合为列表列表，其中每个列表列表都包含来自同一日期(同一天，时间应被忽略)的实体.

I want to regroup them as list of lists which each list of lists contains Entities from the same date (same day, time should be ignored).

如何以 Pythonic 的方式实现这一点?

How can this be achieved in a pythonic way ?

谢谢

推荐答案

创建一个只提取日期的小函数:

Create a small function to extract just the date:

def extract_date(entity):
    'extracts the starting date from an entity'
    return entity.start_time.date()

然后您可以将其与 itertools.groupby:

Then you can use it with itertools.groupby:

from itertools import groupby

entities = Entity.objects.order_by('start_time')
for start_date, group in groupby(entities, key=extract_date):
    do_something_with(start_date, list(group))

或者，如果你真的想要一个列表列表:

Or, if you really want a list of lists:

entities = Entity.objects.order_by('start_time')
list_of_lists = [list(g) for t, g in groupby(entities, key=extract_date)]

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