Django字段中的项目计数

Question

models.py

class Event(models.Model):
    name = models.CharField(max_length=20, unique=True)
    distance = models.IntegerField()
    date = models.DateField()

class Category(models.Model):
    name = models.CharField(max_length=20, unique=True)
    description = models.CharField(max_length=20, unique=True)
    isnew = models.BooleanField(default=False)

class Result(models.Model):
    event = models.ForeignKey(Event)
    category = models.ForeignKey(Category)
    score = models.IntegerField()

我想进行查询以返回给定事件的Result表中每个唯一Category的计数.

我现在正在做的是:

results = Result.objects.filter(event=myevent)
categorycountdict = {}
for r in results:
    if r.category in categorycountdict:
        categorycountdict[r.category] += 1
    else:
        categorycountdict[r.category] = 1

有没有更好的方法,可能是通过查询而不是python.

Answer 1

您可以使用annotate()与values().这种方法显示在文档中values().要获取每个类别名称的计数,您可以执行以下操作:

from django.db.models import Count

categories = Result.objects.filter(
    event=myevent,
).order_by('category').values(
    'category__name'
).annotate(count=Count('category__name'))

这将返回键的词典列表category__name和count,例如:

[{'count': 3, 'category__name': u'category1'}, {'count': 1, 'category__name': u'category2'}]

您可以使用字典理解将其转换为单个字典:

counts_by_category = {d['category__name']: d['count'] for f in categories}