Graphql Newtonsoft serializer throws error while parsing enum

Question

I have a .NET Core GraphQL backend service consumed in a Blazor web assembly app with a GetData GraphQL query with an enum like this:

public enum SomeEnumTypes : byte
{
    None,
    First,
    SecondItem
}

When the data is returned from the backend in that query, SecondItem from enum is returned as SECOND_ITEM to client but it results in an error:

Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
Unhandled exception rendering component: Error converting value "SECOND_ITEM" to type 'SomeEnumTypes'. Path 'data.GetData[0].someEnumType', line 1, position 1375.

Newtonsoft.Json.JsonSerializationException: Error converting value "SECOND_ITEM" to type 'SomeEnumTypes'. Path 'data.GetData[0].someEnumType', line 1, position 1375.

System.ArgumentException: Requested value 'SECOND_ITEM' was not found.

at Newtonsoft.Json.Utilities.EnumUtils.ParseEnum(Type enumType, NamingStrategy namingStrategy, String value, Boolean disallowNumber)
at Newtonsoft.Json.Converters.StringEnumConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)

SomeEnumTypes enum is in a third party nuget library so I can't make any changes to the enum directly.

I tried multiple ways including writing custom converters for the Newtonsoft serializer with regex to handle underscores and even creating a dictionary for that enum to convert in the converter but no use.

_graphqlClient = new GraphQLHttpClient(_configuration.GetValue<string>("SomeKey"), new NewtonsoftJsonSerializer(options =>
{
    options.Converters.Add(new SomeConverter())
}));

Is there something I am missing? Help would be appreciated.

dbc · Accepted Answer · 2025-01-14 21:56:31Z

You appear to have found a bug with GraphQL.Client.Serializer.Newtonsoft:

Json.NET applies converters in the order they are added to the JsonSerializerSettings.Converters list.
NewtonsoftJsonSerializer adds a converter, ConstantCaseEnumConverter, to the beginning of the list, thereby superseding your SomeConverter converter which you add to the end.
ConstantCaseEnumConverter is broken:
- It serializes enums in CONSTANT_CASE but it deserializes them without any case policy at all, so an enum value like SecondItem => SECOND_ITEM cannot be round-tripped.
- It applies its casing policy incorrectly for [Flags] enums, which should be comma-delimited like so: "FLAG_ITEM_ONE, FLAG_ITEM_THREE".

Honestly I can't figure out why GraphQL implemented their converter this way when it would have been much simpler to create a constant case naming strategy and set it on StringEnumConverter.NamingStrategy. I can only guess that they wanted to disable support for EnumMemberAttribute, which is not supported by SystemTextJsonSerializer.

As a workaround, you can create a fixed enum converter and insert it at the beginning of the converters list.

As long as you don't have [EnumMember("some name")] applied to any of your enums, the simplest way to create a fixed converter is to create your own custom naming strategy and use it with the Newtonsoft's built-in StringEnumConverter:

using GraphQL.Client.Abstractions.Utilities;

public sealed class ConstantCaseNamingStrategy : NamingStrategy
{
    protected override string ResolvePropertyName(string name) => name.ToConstantCase();
}

Then insert it at the beginning as follows:

new NewtonsoftJsonSerializer(
    options => 
        options.Converters.Insert(
            0, new StringEnumConverter(new ConstantCaseNamingStrategy())));

And you should be able to round-trip your SomeEnumTypes successfully.

Mockup fiddle here.

This is interesting, I thought it to be too simple of a case to be missed. Thanks for your suggestions seems like have to do what you said.

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