How to use enums with EnumMember attribute in FromBody ViewModel in Web API Request?

Question

I\'m trying to implement an HttpPost method in an ASP.NET Core Web API project with a [FromBody] view model and enums. In the past, binding view models with the

Answer 1

The code from the question that I posted is indeed valid. In my minimal sample, I forgot to set the [Required] attribute on the enum. However, then I had the problem how the method should react if then value is not set. It correctly(?) assumed the default value of the enum which is not what I wanted.

I searched around and found this solution https://stackoverflow.com/a/54206737/225808 The enum is nullable which is not ideal but at least I have the validation and I get an error message if the value is missing

Update/Warning: You can use the solution referenced above, but! It seems that the code will compile but instead throws the error message from question. I further compared my own project with the test project and noticed that I also needed two include 2 NuGet packages in order to make everything work:

• Microsoft.AspNetCore.Mvc.NewtonsoftJson
• Newtonsoft.Json

It seems that Microsoft.AspNetCore.Mvc.NewtonsoftJson overrides from default behavior? If someone can shed some light on this, I'd glady appreciate it.

Update 2: I also updated the referenced so solution to parse the enum value based on the EnumMemberAttribute:

[JsonConverter(typeof(CustomStringToEnumConverter<WeatherEnum>))]
public enum WeatherEnum
{
    [EnumMember(Value = "123good")]
    Good,

    [EnumMember(Value = "bad")]
    Bad
}

public class CustomStringToEnumConverter<T> : StringEnumConverter
{
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (string.IsNullOrEmpty(reader.Value?.ToString()))
        {
            return null;
        }
        try
        {
            return EnumExtensions.GetValueFromEnumMember<T>(reader.Value.ToString());
        }
        catch (Exception ex)
        {
            return null;
        }
    }
}

public static class EnumExtensions
{
    public static T GetValueFromEnumMember<T>(string value)
    {
        var type = typeof(T);
        if (!type.IsEnum) throw new InvalidOperationException();
        foreach (var field in type.GetFields())
        {
            var attribute = Attribute.GetCustomAttribute(field,
                typeof(EnumMemberAttribute)) as EnumMemberAttribute;
            if (attribute != null)
            {
                if (attribute.Value == value)
                    return (T)field.GetValue(null);
            }
            else
            {
                if (field.Name == value)
                    return (T)field.GetValue(null);
            }
        }
        throw new ArgumentException($"unknow value: {value}");
    }
}