如何在Django中执行联接和聚合计数 [英] How to perform a join and aggregate count in Django

问题描述

我有两个模型：

class Unit (models.Model):
    Unit_name = models.CharField(max_length=30)
    Hull_number = models.CharField(max_length=30)
    Parent_unit = models.ForeignKey("self", blank=True, null=True)
    Class = models.ForeignKey(Class)
    email = models.CharField(max_length=50, default='')
    Member = models.ManyToManyField(Member, through='MemberUnit')

    def __str__(self):
        return self.Unit_name

class MemberUnit(models.Model):
    Member = models.ForeignKey(Member)
    Unit = models.ForeignKey(Unit)
    Position = models.ForeignKey(ClassPosition)

    def __str__(self):
        return self.Unit.Unit_name + " " + 
                self.Position.unit_position.Position_name + " ( " + 
                self.Member.first_name + " " + self.Member.last_name + " )"

我是Django的新手。查询是我所缺少的。
我需要的是Unit_name的总数。

I am new to Django (sort of). Querying is where I am lacking. What I need is a aggregate count of Unit_names.

为此，我需要在查询中提供一个Unit_Name及其数量作为查询的一部分。
在此方面的任何协助将不胜感激。

To that end, I require a query as part of my view to provide a Unit_Name and it's count. Any Assistance on this would be greatly appreciated.

谢谢

推荐答案

希望这会有所帮助：

from django.db.models import Count
MemberUnit.objects.values('Unit__Unit_name').annotate(c=Count('Unit'))

您可以在Django的shell：

You can try this in Django's shell:

manage.py shell

请参见文档

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