在Django中如何正确执行GraphQL的Mutation查询？

问题描述 #

在Django中定义了Customer模型、CustomerNode及CreateCustomerMutation等GraphQL相关代码后，尝试两种Mutation查询均报错：

• Query1提示参数'name'和'address'不存在
• Query2提示参数'input'不存在

相关代码 #

# Model
class Customer(models.Model):
    name = models.CharField(max_length=150)
    address = models.CharField(max_length=150)

# Node
class CustomerNode(DjangoObjectType):
    class Meta:
        model = Customer
        interfaces = (relay.Node,)


# Mutations
class CreateCustomerMutation(relay.ClientIDMutation):
    class Input:
        name = graphene.String(required=True)
        address = graphene.String()

    customer = graphene.Field(CustomerNode)

    @classmethod
    def mutate_and_get_payload(cls, root, info, **input):
        customer_instance = Customer(
            name=input["name"],
            address=input["address"],
        )
        customer_instance.save()
        return CreateCustomerMutation(customer=customer_instance)

class Mutation(ObjectType):
    create_customer = graphene.Field(CreateCustomerMutation)

# Schema
schema = graphene.Schema(query=Query, mutation=Mutation)

尝试的查询 #

# Query 1
mutation {
   createCustomer(name: "John", address: "Some address") {
     id, name
   }
}
# Query 2
mutation {
   createCustomer(input: {name: "John", address: "Some address"}) {
     id, name
   }
}

报错信息 #

# Query 1
"Unknown argument 'name' on field 'Mutation.createCustomer'."
"Unknown argument 'address' on field 'Mutation.createCustomer'."

# Query 2
"Unknown argument 'input' on field 'Mutation.createCustomer'."

错误原因 #

问题出在Mutation的注册方式：使用relay.ClientIDMutation时，不能直接用graphene.Field()声明字段，必须调用CreateCustomerMutation.Field()方法。ClientIDMutation内部会自动处理input参数的结构，直接用graphene.Field()无法生成正确的字段定义，导致GraphQL无法识别传入的参数。

修复步骤 #

修改Mutation类中create_customer字段的定义：

class Mutation(ObjectType):
    # 替换原来的 graphene.Field(CreateCustomerMutation)
    create_customer = CreateCustomerMutation.Field()

正确的查询语法 #

修复后，必须使用input参数包裹所有字段，同时注意返回结构需要先获取customer字段，再访问其属性：

mutation {
   createCustomer(input: {name: "John", address: "Some address"}) {
     customer {
       id, name, address
     }
   }
}

说明：relay.ClientIDMutation的返回值是包含你定义的customer字段的对象，因此不能直接在createCustomer下取id、name，必须嵌套一层customer。

内容的提问来源于stack exchange，提问作者HappyChappy