Django，用具有最低参数的多对多字段元素的id注释字段

Question

我有以下型号:

from django.db import models

class Topping(models.Model):
    # ...
    price = models.IntegerField()

class Pizza(models.Model):
    # ...
    toppings = models.ManyToManyField(Topping)

我需要得到以下查询:

my_query = Pizza.objects.all().annotate(
                            topping_with_min_price="get id of topping with the minimal price")

那么，如何获得呢？

Answer 1

您可以使用子查询:

from django.db.models import <strong>OuterRef, Subquery</strong>

my_query = Pizza.objects.annotate(
    topping_with_min_price=Subquery(
        <strong>Topping.objects.filter(
            pizza=OuterRef('pk')
        ).order_by('price').values('pk')[:1]</strong>
    )
)