Django Rest Framework，如何获取另一个外键内外键的对象数量

Question

我有三个模型Store，Product并且Orderclass Store(models.Model):    ......class Product(models.Model):    store = models.ForeignKey(Store, ...)class Order(models.Model):    product = models.ForeignKey(Product ...)    delivered = models.BooleanField()我想创建一个@property模型Store来计算包含其产品的订单数，并且还包含delivered=True我将如何去做呢？

Answer 1

在您的商店模型中property照常定义

class Store(models.Model):

    ......

    

    @property

    def order_count(self):

        return Order.objects.filter(product__store=self, delivered=True).count()

class Product(models.Model):

    store = models.ForeignKey(Store, ...)

class Order(models.Model):

    product = models.ForeignKey(Product ...)

    delivered = models.BooleanField()

然后在序列化器中，您有两种方法将该order_count属性包含在序列化器中 -

定义一个SerializerMethodField在StoreSerializer

class StoreSerializer(serializers.ModelSerializer):

   order_count = serilizers.SerializerMethodField()

   def get_order_count(self, instance):

       return instance.order_count # the property in store object

   class Meta:

       model = Store

       fields = ['other', 'fields', 'in', 'store', 'model', 'order_count']

声明order_count为ReadOnlyField您的StoreSerializer

class StoreSerializer(serializers.ModelSerializer):

    order_count = serilizers.ReadOnlyField()

    class Meta:

        model = Store

        fields = ['other', 'fields', 'in', 'store', 'model', 'order_count']