为什么 graphql-dotnet 会为此模式返回 "Expected non-null value" 错误？

Question

我有一个简单的模式，我正尝试按如下方式查询：

{
  subQuery {
    subObjectGraph {
      Name
    }
  }
}

但是 "graphiql" 抛出以下错误，甚至运行我的查询似乎都没有。

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

我的模式（如下）有什么问题？我正在新建一个子对象，所以我不明白为什么错误消息暗示该值为空。

    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);
        }
    }

如果我用 StringGraphType 替换 MySubObjectGraphType，代码工作正常，所以问题一定出在 MySubObjectGraphType 的配置上。

请帮忙？我正在使用 v2.4。

Answer 1

您正在 return在您的 RootQuery 的子查询中创建 GraphType。解析器应该只 return DTO 而不是 GraphTypes。

如果您尝试组织查询，那么只需 return 一个空对象。

Field<MySubQuery>(
  name: "subQuery",
  resolve: ctx => new {});

https://graphql-dotnet.github.io/docs/getting-started/query-organization

Answer 2

您需要在 Startup.cs

中为 MySubObjectGraphType 添加服务注册

所以规则可以描述为"custom types deriving from ObjectGraphType must be registered via dependency injection at some point"

例如 Startup.cs：

services.AddSingleton<MySubObjectGraphType>();

为什么 graphql-dotnet 会为此模式返回 "Expected non-null value" 错误？

Why is graphql-dotnet returning "Expected non-null value" error for this schema?

c#

graphql

graphql-dotnet