An error "JSON cannot deserialize the given value." when use Federation and JsonType properties in the models of internal service

Is there an existing issue for this?

• I have searched the existing issues

Product

Hot Chocolate

Describe the bug

Hey guys. I have occured with strange behavior when using JsonType and federation. So I have model on the internal service:

public class MyModel
{
    public long Id { get; set; }

    [GraphQLType(typeof(JsonType))]
    public string MyJson{ get; set; }
}

MyJson actually is List<Hours>. But in database it is stored like json string.

public class Hours
{
    public DayOfWeek Day { get; set; }
    public bool IsActive { get; set; }
    public TimeSpan? From { get; set; }
    public TimeSpan? To { get; set; }
}

When I’m fetching MyModel directly from internal service - it works fine, I recieve normal json response, but when I’m trying to fetch data via my external service, that is stitched with internal one, it says “JSON cannot deserialize the given value.”

Steps to reproduce

1. Configuration of internal service:

• Model

public class MyModel
{
    public long Id { get; set; }

    [GraphQLType(typeof(JsonType))]
    public string MyJson{ get; set; }
}

• Query

[QueryType]
public class MyModelQueries
{
    [UsePaging(IncludeTotalCount = true)]
    [UseProjection]
    [UseFiltering]
    [UseSorting]
    public IQueryable<MyModel> MyModelSearch([Service] IMyModelRepository repository)
    => repository.EntitySearch();
}

• Startup

        services.AddMemoryCache();
        services.AddGraphQLServer()
                .AddServiceTypes()
                .AddType(new TimeSpanType(TimeSpanFormat.DotNet))
                .AddProjections()
                .AddFiltering()
                .AddSorting()
                .AddInMemorySubscriptions()
                .InitializeOnStartup()
                .PublishSchemaDefinition(c => c
                  .SetName("InternalService"));

1. Configuration of external service:

• Startup

        services.AddHttpClient(
            "InternalService",
            c => c.BaseAddress = new Uri($"{InternalServiceUrl}/graphql"))

        services.AddGraphQLServer()
                .AddRemoteSchema("InternalService")
                .AddType(new TimeSpanType(TimeSpanFormat.DotNet));

1. Make query on external service with fetching MyJson, that leads to “JSON cannot deserialize the given value.” errror in response.

Relevant log output

No response

Additional Context?

Platform: .Net6 Database: PostgreSQL EFCore: Npgsql.EntityFrameworkCore.PostgreSQL 7.0.1 HotChocolate: 13.3.3

Version

13.3.3

[mvarendorff]

Given that Stitching is still very much at the forefront of the documentation, I feel like this is a bit harsh. Arguably, I am biased, since I am facing the same problems as OP but two YouTube videos aside there is nothing available on Fusion yet:

Is there really no chance this could be looked at?

[Vespersion]

I’ve also run into this issue, and given that it looks like this will never be looked at, and until Fusion has some better documentation and we can switch to it, I’ve found an intermediary solution.

In my case I was using the JSON type, with my underlying field being a JsonElement. What seems to be the problem is that the downstream service returns a JsonElement to the stitching request, but this response result is all serialized to a Dictionary, which means that the full JsonElement object is converted to a dictionary. In this case the stitching code doesn’t seem to handle this situation and can’t turn a dictionary into a JsonElement. I haven’t used a string with the Json type but I imagine the problem is the same.

I’ve created an IHttpStitchingRequestInterceptor to intercept the stitching response from the downstream service. Notably the OnReceivedResultAsync() method takes an IQueryResult argument which contains the data dictionary and returns an IQueryResult, which will override the result value with your returned value.

From here I just converted the dictionary representation of the JsonElement into an actual JsonElement and replaced the value in the result. Obviously the hard part here is finding the correct value in the result, but the method also takes an IQueryRequest which describes the query.

Extremely simplified code below(probably a better way to convert from Dictionary to JsonElement but in my case I know my Json value is not nested):

public class GatewayHttpStitchingRequestInterceptor : IHttpStitchingRequestInterceptor
{
    public GatewayHttpStitchingRequestInterceptor()
    {
    }

    public ValueTask OnCreateRequestAsync(string targetSchema, IQueryRequest request, HttpRequestMessage requestMessage, CancellationToken cancellationToken = default)
    {
        return default;
    }

    public ValueTask<IQueryResult> OnReceivedResultAsync(string targetSchema, IQueryRequest request, IQueryResult result, HttpResponseMessage responseMessage, CancellationToken cancellationToken = default)
    {
        var entity = ((Dictionary<string, object>)result.Data["myEntity"]);
        var jsonValueDict = ((Dictionary<string, object>)entity["jsonField"]).ToDictionary(x => x.Key, x => ((IValueNode)x.Value).Value);
        var jsonValue = JsonSerializer.SerializeToDocument<Dictionary<string, object>>(jsonValueDict).RootElement;
        entity["jsonField"] = jsonValue;
        return new ValueTask<IQueryResult>(result);
    }
}

// Startup.cs

services.AddSingleton<IHttpStitchingRequestInterceptor, GatewayHttpStitchingRequestInterceptor>();

If my solution doesn’t exactly solve your problem, you can at least use the stitching interceptor to debug what might be wrong with the result.