Using [FromQuery] to parse enum values - asp.net-core

Question

I'm using the [FromQuery] attribute to parse a Get requests arguments into a complex object. For example:
[HttpGet("some-get-request")]
public IActionResult DoSomething([FromQuery] SomeArguments someArgs)
{
}
One of the properties of the SomeArguments object is an enum.
public enum SomeEnum { EnumValue01, EnumValue02 }
public class SomeArguments
{
[FromQuery(Name = "enum_arg")]
public SomeEnum EnumArgument { get; set; }
}
And I call the endpoint with something like:
http://localhost:1234/api/some-controller/some-get-request?enum_arg=EnumValue01
And this all works great. However, I want to be able to use a different enum value in the URL than in my C# enum value. For example, I want to call using a URL such as
http://localhost:1234/api/some-controller/some-get-request?enum_arg=eval01
How can I do this?
I thought I could use the [FromQuery] attribute, like I can with properties, but that doesnt seem to be possible:
'FromQuery' is not valid on this declaration type. It is only valid on 'property, indexer, parameter'

Answer 1

You can use EnumMemberAttribute in conjunction with StringEnumConverter to achieve your goal. Define SomeEnum as following
[JsonConverter(typeof(StringEnumConverter))]
public enum SomeEnum
{
[EnumMember(Value = "eval01")]
EnumValue01,
[EnumMember(Value = "eval02")]
EnumValue02
}
At this point it will work as you need only when Newtonsoft json serializer is used. For example, when controller expects POST request and parameter is marked as [FromBody]. In your case it won't work yet because during binding of [FromQuery] parameter json serializer is not used. To solve this one create custom model binder
public class JsonModelBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
string rawData = bindingContext.ValueProvider.GetValue(bindingContext.ModelName).FirstValue;
rawData = JsonConvert.SerializeObject(rawData); //turns value to valid json
try
{
SomeEnum result = JsonConvert.DeserializeObject<SomeEnum>(rawData); //manually deserializing value
bindingContext.Result = ModelBindingResult.Success(result);
}
catch (JsonSerializationException ex)
{
//do nothing since "failed" result is set by default
}
return Task.CompletedTask;
}
}
Update SomeEnum definition to use JsonModelBinder
[JsonConverter(typeof(StringEnumConverter))]
[ModelBinder(typeof(JsonModelBinder))]
public enum SomeEnum