如何根据查询集中的值为对象分配排名

Question

我有一个查询集，它返回菜单列表，我想根据累积的票数为每个菜单分配一个排名。有没有办法使用django查询表达式来实现这一点？我也愿意接受任何其他建议。

查询集如下：

qs=Menu.objects.filter(Q(created_at__date__iexact=todays_date((.order_by('-votes'(

菜单类模型如下所示：

class Menu(models.Model):
"""Represents menu class model"""
restaurant = models.ForeignKey(Restaurant,null=True,blank=True,on_delete=models.CASCADE)
file = models.FileField(upload_to='menus/')
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
uploaded_by = models.CharField(max_length=50, null=True, blank=True)
votes = models.IntegerField(default=0)

序列化后，查询集返回以下数据：

[
{
"id": 10,
"file": "https://res.cloudinary.com/dw9bllelz/raw/upload/v1/media/menus/index_ah660c.jpeg",
"restaurant": "Burger King",
"votes": 10,
"created_at": "2021-06-03T09:33:05.505482+03:00"
},
{
"id": 9,
"file": "https://res.cloudinary.com/dw9bllelz/raw/upload/v1/media/menus/index_ah660c.jpeg",
"restaurant": "Texas Plates",
"votes": 2,
"created_at": "2021-06-03T09:33:05.505482+03:00"
},
{
"id": 8,
"file": "https://res.cloudinary.com/dw9bllelz/raw/upload/v1/media/menus/index_ah660c.jpeg",
"restaurant": "Carlito Dishes",
"votes": 2,
"created_at": "2021-06-03T09:33:05.505482+03:00"
},
{
"id": 7,
"file": "https://res.cloudinary.com/dw9bllelz/raw/upload/v1/media/menus/index_ah660c.jpeg",
"restaurant": "Kram Dishes",
"votes": 1,
"created_at": "2021-06-03T09:33:05.505482+03:00"
},
]

Answer 1

您可以使用数组中对象的索引作为其索引，也可以使用Window函数[Django-docs]并使用Rank或DenseRank(参考[Django-docs](函数根据需要计算秩：

from django.db.models import F, Window
from django.db.models.functions import Rank

qs = Menu.objects.filter(
Q(created_at__date__iexact=todays_date)
).annotate(
rank=Window(
expression=Rank(),
order_by=F('votes').desc(),
)
)

for menu in qs:
print(menu.rank, menu.votes)