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，它返回一个菜单列表，我想根据累积的票数为每个菜单分配一个排名有没有一种方法可以使用 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')

Menu类模型如下图所示：

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)

查询集序列化后返回如下数据：

[
  {
        "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 index 作为其索引，也可以使用Window functions [Django docs] 并使用Rank 或DenseRank (Reference [Django docs]) 函数来计算根据您的需要排名：

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)