为什么graphql-dotnet会为此模式返回“预期非空值”错误？

Question

我有一个要查询的简单架构，如下所示：

{
  subQuery {
    subObjectGraph {
      Name
    }
  }
}

但是“ graphiql”抛出以下错误，甚至没有运行我的查询。

{
  "errors": [
    {
      "message": "Expected non-null value, resolve delegate return null for \"$Api.Schema.Queries.MySubObjectGraphType\"",
      "extensions": {
        "code": "INVALID_OPERATION"
      }
    }
  ]
}

我的架构有什么问题（如下）？我正在新建一个SubObject，所以我不明白为什么错误消息暗示该值为null。

    public class Schema: GraphQL.Types.Schema
    {
        public Schema(IDependencyResolver resolver): base(resolver)
        {
            Query = resolver.Resolve<RootQuery>();  
            Mutation = null;
        }
    }

    public class RootQuery: ObjectGraphType
    {
        public RootQuery(IDependencyResolver resolver)
        {
            Name = "Query";

            Field<MySubQuery>(
                name: "subQuery",
                resolve: ctx => resolver.Resolve<MySubQuery>());
        }
    }


    public class MySubQuery: ObjectGraphType
    {
        public MySubQuery()
        {
            Name = "TempSubQuery";

            Field<StringGraphType>("SubQueryName", resolve: ctx => "Some string value");

            Field<MySubObjectGraphType>(
                name: "subObjectGraph",
                resolve: ctx => FetchFromRepo());
        }


        //Repo access would go here, but just new-ing the object for now.
        private SubObject FetchFromRepo()
        {
            return new SubObject() { Name = "some sub object" };
        }
    }


    public class SubObject
    {
        public string Name { get; set; }
    }

    public class MySubObjectGraphType: ObjectGraphType<SubObject>
    {
        public MySubObjectGraphType()
        {
            Name = "MySubObject";
            Description = "An object with leaf nodes";

            Field(l => l.Name);
        }
    }

如果将MySubObjectGraphType替换为StringGraphType，则代码可以正常工作，因此问题必须出在MySubObjectGraphType的配置上。

请帮忙？我正在使用v2.4。

Answer 1

您需要添加一个服务注册为MySubObjectGraphType您的Startup.cs

因此，该规则可以描述为“ ObjectGraphType必须在某个时候通过依赖注入来注册源自的自定义类型”

例如在Startup.cs：

services.AddSingleton<MySubObjectGraphType>();