I am migrating an old .NET 4.8 Web API to .NET 6 and realized an issue with Json conversion. For example, this is an example Web API in .NET 4.8:

    public enum SampleEnum
    {
        Bar,
        Baz,
    }
    public class Jerry
    {
        public SampleEnum MyEnum { get; set; }
    }
    public class ValuesController : ApiController
    {

        // POST api/values
        public void Post([FromBody] Jerry value)
        {
            var a = value;
        }
    }

If the request is one with clearly wrong value:

{  
   "MyEnum":  "MonthEnd"       
}

Above webapi in .net 4.8 will use the default value for the enum (Bar).

For the same code in .net 6 with NewtonJson or Json.Text, it will throw exception saying I can't understand MonthEnd.

.net 6 is the right behaviour as the user passed a wrong value, but my problem is that our webapi is already on production for very long and we can't risk a sudden surge of customer complain.

Is there a way to mimic the .net 4.8's behaviour (i.e. if an enum value can't be understood, we fallback to deafult )?

CodePudding user response：

You can workaround with custom converter. For example something like the following:

class CustomEnumConverter<T> : JsonConverter<T> where T: struct, Enum
{
    public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (Enum.TryParse<T>(reader.GetString(), out var r))
        {
            return r;
        }
        return default;
    }
    
    public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options) => writer.WriteStringValue(value.ToString("G"));
}

And then mark corresponding property with it:

public class Jerry
{
    [JsonConverter(typeof(CustomEnumConverter<SampleEnum>))]
    public SampleEnum MyEnum { get; set; }
}

Or if you need to do it globally - create a converter factory which will reuse this converter.