price() 缺少 1 个必需的位置参数：'self'尝试在 Django Rest 框架中计算价格

Question

我试图创建一个案例，当我调用订单创建api时，价格将自行计算并保存在数据库中，但我在邮递员中收到了这个错误。

错误：price((缺少1个必需的位置参数：'self

我的型号：

class Order(models.Model):

user = models.ForeignKey(User, on_delete=models.CASCADE, blank=True)   
ordered_date = models.DateTimeField(auto_now_add=True)
ordered = models.BooleanField(default=False)
total_price = models.CharField(max_length=50,blank=True,null=True)
#billing_details = models.OneToOneField('BillingDetails',on_delete=models.CASCADE,null=True,blank=True,related_name="order")
def __str__(self):
return self.user.email

def price(self):
total_item_price = self.quantity * self.item.varaints.price
return total_item_price
class OrderItem(models.Model):
#user = models.ForeignKey(User,on_delete=models.CASCADE, blank=True
#orderItem_ID = models.UUIDField(max_length=12, editable=False,default=str(uuid.uuid4()))
orderItem_ID = models.CharField(max_length=12, editable=False, default=id_generator)
order = models.ForeignKey(Order,on_delete=models.CASCADE, blank=True,null=True,related_name='order_items')
item = models.ForeignKey(Product, on_delete=models.CASCADE,blank=True, null=True)
order_variants = models.ForeignKey(Variants, on_delete=models.CASCADE,blank=True,null=True)
quantity = models.IntegerField(default=1)
total_item_price = models.PositiveIntegerField(blank=True,null=True,default=price())
ORDER_STATUS = (
('To_Ship', 'To Ship',),
('Shipped', 'Shipped',),
('Delivered', 'Delivered',),
('Cancelled', 'Cancelled',),
)
order_item_status = models.CharField(max_length=50,choices=ORDER_STATUS,default='To_Ship')

这里，数量字段存在于OrderItem模型本身中，但价格存在于与这样的Product模型相关的Variant模型中。

我尝试过的东西：

1. 我试着去掉价格中的括号((，但得到了同样的错误
2. 如果我尝试在total_itel_price字段之前的类模型中放入price函数，它会说在price的括号内需要self，如果我放入self，=是必需的，并且我不知道放入price(self=？(

其他型号：

Class Variants(models.Model):
...#other fields    
price = models.DecimalField(decimal_places=2, max_digits=20,default=500)
Class Product(models.Model):
...#other fields
variants = models.ManyToManyField(Variants,related_name='products')

我的序列化程序：

class OrderSerializer(serializers.ModelSerializer):
billing_details = BillingDetailsSerializer()
order_items = OrderItemSerializer(many=True)
user = serializers.PrimaryKeyRelatedField(read_only=True, default=serializers.CurrentUserDefault())
class Meta:
model = Order
fields = ['id','user','ordered_date','order_status', 'ordered', 'order_items', 'total_price','billing_details']
# depth = 1   
def create(self, validated_data):
user = self.context['request'].user
if not user.is_seller:
order_items = validated_data.pop('order_items')
billing_details = validated_data.pop('billing_details')
order = Order.objects.create(user=user,**validated_data)
BillingDetails.objects.create(user=user,order=order,**billing_details)
for order_items in order_items:
OrderItem.objects.create(order=order,**order_items)

else:
raise serializers.ValidationError("This is not a customer account.Please login as customer.")

更新代码：

class OrderItem(models.Model):   

#total_item_price = models.PositiveIntegerField(blank=True,null=True,default=0) #commented out this field other fields are same as above

order_item_status = models.CharField(max_length=50,choices=ORDER_STATUS,default='To_Ship')
@property
def price(self):
return self.quantity * self.item.varaints.price
class OrderItemSerializer(serializers.ModelSerializer):    
order = serializers.PrimaryKeyRelatedField(read_only=True)
price = serializers.ReadOnlyField()
class Meta:
model = OrderItem
fields = ['id','order','orderItem_ID','item','order_variants', 'quantity','order_item_status','price']
# depth = 1

订单序列化程序和上面一样。它包括OrderItemSerializer，如图所示：

class OrderSerializer(serializers.ModelSerializer):
billing_details = BillingDetailsSerializer()
order_items = OrderItemSerializer(many=True)
user = serializers.PrimaryKeyRelatedField(read_only=True, default=serializers.CurrentUserDefault())
class Meta:
model = Order
fields = ['id','user','ordered_date','order_status', 'ordered', 'order_items', 'total_price','billing_details']

更新订单总价格计算

这是我为total_price计算所做的，但我在api响应中没有得到total_price字段，但没有错误。

class Order(models.Model):     
.....#same fields as above
@property
def total_order_price(self):
return sum([_.price for _ in self.order_items_set.all()])

我在OrderItem模型中使用了price函数，我的OrderItem实例是order_items。问题出在哪里？？

Answer 1

试试这个

class Order(models.Model):
"""Stores the details of the order"""
user: User = models.ForeignKey(User, on_delete=models.CASCADE, blank=True)
ordered_date = models.DateTimeField(auto_now_add=True)
ordered = models.BooleanField(default=False)
# billing_details = models.OneToOneField('BillingDetails',on_delete=models.CASCADE,null=True,blank=True,related_name="order")
def __str__(self) -> str:
return self.user.email
@property
def total_price(self) -> int:
"""
Dropped the total price field and created it as property
This is not the best practice, I am leaving that as practice for you :)
"""
return sum([_.total_item_price for _ in self.orderitem_set.all()])

class OrderItem(models.Model):
"""Order Item stores the details of the each order item"""
orderItem_ID: str = models.CharField(
max_length=12, editable=False, default=id_generator
)
order: Order = models.ForeignKey(
Order,
on_delete=models.CASCADE,
blank=True,
null=True,
related_name="order_items",
)
item: Product = models.ForeignKey(
Product, on_delete=models.CASCADE, blank=True, null=True
)
order_variants: Variants = models.ForeignKey(
Variants, on_delete=models.CASCADE, blank=True, null=True
)
quantity: int = models.IntegerField(default=1)
price = models.PositiveIntegerField()
@property
def total_item_price(self):
"""
Calculates total item price for the item
Here you can also add additional logics such as
taxes per item etc
"""
return self.price * self.quantity
ORDER_STATUS = (
("To_Ship", "To Ship"),
("Shipped", "Shipped"),
("Delivered", "Delivered"),
("Cancelled", "Cancelled"),
)
order_item_status = models.CharField(
max_length=50, choices=ORDER_STATUS, default="To_Ship"
)

Answer 2

此代码最终适用于OrderItem价格计算：

class OrderItem(models.Model): 
.....#fields same as above
#total_item_price = models.PositiveIntegerField(blank=True,null=True,default=0)
ORDER_STATUS = (
('To_Ship', 'To Ship',),
('Shipped', 'Shipped',),
('Delivered', 'Delivered',),
('Cancelled', 'Cancelled',),
)
order_item_status = models.CharField(max_length=50,choices=ORDER_STATUS,default='To_Ship')
@property
def price(self):
total_item_price = self.quantity * self.order_variants.price
return total_item_price

变体中有一个拼写错误。此外，我应该使用order_variants而不是item.variants，因为item有很多变体，但用户只选择一个具有唯一价格的变体。