GraphQL - Execution Error (The parent cannot be cast to..)

Question

I am trying to implement GraphQL in web API. The method is working fine when return object type. But it is throwing an error while I am trying to return Object List.

    public class MyData
    {
       public int Code { get; set; }
       public string Name { get; set; }
       public string LastName { get; set; }
       public string City { get; set; }
       public string State { get; set; }
       public string Country { get; set; }
   }

Query.cs

     public List<MyData> GetList()
     {
         List<MyData> myList = null;

         string query = "select Code, Name, LastName,  City, State, Country from MyTable";

         using (var connection = new MySqlConnection(connectionString))
         {
              myList = connection.Query<MyData>(query).ToList();
          }
          return myList;
      }

    public class QueryObjectType : ObjectType<Query>
    {
         descriptor.Field(g => g.GetList())
        .Type<MyDataDataObjectType>().Name("GetList");
    }
    
    public class MyDataDataObjectType: ObjectType<MyData>
    {
        protected override void Configure(IObjectTypeDescriptor<MyData> descriptor)
        {
            descriptor.Field(g => g.Code).Type<IntType>().Name("Code");
            descriptor.Field(g => g.Name).Type<StringType>().Name("Name");
            descriptor.Field(g => g.LastName).Type<StringType>().Name("LastName");
            descriptor.Field(g => g.City).Type<StringType>().Name("City");
            descriptor.Field(g => g.State).Type<IntType>().Name("State");
            descriptor.Field(g => g.Country).Type<IntType>().Name("Country");
         }
    }

startup.cs

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddGraphQLServer()
        .AddQueryType<QueryObjectType>();
    }
    
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
            app.UseGraphQLVoyager(new VoyagerOptions()
            {
                GraphQLEndPoint = "/graphql"
        }, "/graphql-ui");
    }

The GetList() methods is returning the list with object data of type MyData. But in the Insomnia client showing an error. I think something wrong with the below code

         descriptor.Field(g => g.GetList())
        .Type<MyDataDataObjectType>().Name("GetList");

I am sending the following in the POST call

query{
      a:GetList
      {
         Code
       }
     }

Error:

{ "errors": [ { "message": "Unexpected Execution Error", "locations": [ { "line": 4, "column": 4 } ], "path": [ "a", "Code" ], "extensions": { "message": "The parent cannot be cast to MyData.", "stackTrace": " at HotChocolate.Execution.Processing.MiddlewareContext.SourceT\r\n at HotChocolate.Execution.Processing.MiddlewareContext.ParentT\r\n at lambda_method65(Closure , IResolverContext )\r\n at HotChocolate.Types.FieldMiddlewareCompiler.<>c__DisplayClass3_0.<b__0>d.MoveNext()\r\n--- End of stack trace from previous location ---\r\n at HotChocolate.Execution.Processing.ResolverTask.ExecuteResolverPipelineAsync(CancellationToken cancellationToken)\r\n at HotChocolate.Execution.Processing.ResolverTask.TryExecuteAsync(CancellationToken cancellationToken)" } } ], "data": { "a": { "Code": null } } }

Thanks in advance for your help.

Tobias Tengler · Accepted Answer · 2021-07-27 03:58:55Z

1

You should be seeing an exception in the server that would've told you what is wrong. What I can see is that the type of the field you are specifying is wrong. When returning a List you need to use the ListType:

descriptor.Field(g => g.GetList())
        .Type<ListType<MyDataDataObjectType>>().Name("GetList");

Learn more about this in the lists documentation

answered Jul 27, 2021 at 3:58

Tobias Tengler

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1 Comment

Ullan Over a year ago

Thanks, again getting the same error, something wrong with my implementation. Let me understand the documentation

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