django - 我将如何在 Django 中执行此查询？

Question

假设我有三个模型:User、CarBrand、CarModel、CarCharacteristics。 CarCharacteristics 模型描述了用户如何评价汽车的特性。因此，一个用户可以有许多 CarCharacteristics 对象，并且一个用户可以有许多 CarCharacteristics。

这就是我的模型的样子:

class User(models.Model):
    id = models.AutoField(primary_key=True)

class CarBrand(models.Model):
    idcar_brand = models.AutoField(primary_key=True)

class CarModel(models.Model):
    idcar_model = models.AutoField(primary_key=True)
    car_brand = models.ForeignKey(CarBrand, null=True, on_delete=models.SET_NULL)

class CarCharacteristics(models.Model):
    idcar_characteristics = models.AutoField(primary_key=True)
    user = models.ForeignKey(User, on_delete=models.PROTECT)
    car_model = models.ForeignKey(CarModel, on_delete=models.PROTECT)

我想做的是获取User具有CarCharacteristics的所有CarBrand对象。这就是我现在正在做的事情:

car_chars = CarCharacteristics.objects.filter(user=user_id)
car_brands_ids = []
for car_char in car_chars:
    brand_id = car_char.car_model.car_brand.idcar_brand
    if brand_id not in car_brands_ids:
        car_brands_ids.append(brand_id)
brands = CarBrand.objects.filter(idcar_brand__in=brand_ids)

有更简单的方法吗？如何获取存在 CarCharacteristics 的所有 CarModels？

Answer 1

试试这个:

CarBrand.objects.exclude(carmodel__carcharacteristics__user=None).distinct()