生成笛卡尔乘积的Django注释

from django.db import models
from django.db.models import annotations

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.FloatField()

class Category(models.Model):
    name = models.CharField(max_length=100)
    products = models.ManyToManyField(Product)

@annotations.register
class CartesianProduct(annotations.Annotation):
    def __init__(self, *expressions, **extra):
        self.expressions = expressions
        self.extra = extra

    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False):
        resolved_expressions = []
        for expression in self.expressions:
            resolved_expression = expression.resolve_expression(query, allow_joins, reuse, summarize)
            resolved_expressions.append(resolved_expression)
        return self.copy()

    def as_sql(self, compiler, connection):
        # Generate the SQL for the Cartesian product using the CROSS JOIN
        sql_parts = []
        for expression in self.expressions:
            sql, params = expression.as_sql(compiler, connection)
            sql_parts.append(sql)
        return " CROSS JOIN ".join(sql_parts), []

def cartesian_product(*expressions, **extra):
    return CartesianProduct(*expressions, **extra)

from myapp.models import Category, Product

# 查询所有分类和产品的笛卡尔乘积
categories_with_products = Category.objects.annotate(products_cartesian=cartesian_product('products'))