ASP.NET MVC Core API Serialize Enums to String

How to serialize Enum fields to String instead of an Int in ASP.NET MVC Core 3.0? I'm not able to do it the old way.

services.AddMvc().AddJsonOptions(opts =>
{
    opts.JsonSerializerOptions.Converters.Add(new StringEnumConverter());
})

I'm getting an error:

> cannot convert from 'Newtonsoft.Json.Converters.StringEnumConverter' > to 'System.Text.Json.Serialization.JsonConverter'

New System.Text.Json serialization

ASP.NET MVC Core 3.0 uses built-in JSON serialization. Use System.Text.Json.Serialization.JsonStringEnumConverter (with "Json" prefix):

services
    .AddMvc()
    // Or .AddControllers(...)
    .AddJsonOptions(opts =>
    {
        var enumConverter = new JsonStringEnumConverter();
        opts.JsonSerializerOptions.Converters.Add(enumConverter);
    })

More info here. The documentation can be found here.

If you prefer Newtonsoft.Json

You can also use "traditional" Newtonsoft.Json serialization:

Install-Package Microsoft.AspNetCore.Mvc.NewtonsoftJson

And then:

services
    .AddControllers()
    .AddNewtonsoftJson(opts => opts
        .Converters.Add(new StringEnumConverter()));

some addition:
if use Newtonsoft.Json

Install-Package Microsoft.AspNetCore.Mvc.NewtonsoftJson

services
    .AddControllers()
    .AddNewtonsoftJson(options =>
        options.SerializerSettings.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter()));

options.SerializerSettings.Converters

SerializerSettings is necessary

If you have a Minimal API this will be useful:

using System.Text.Json.Serialization;

builder.Services.Configure<Microsoft.AspNetCore.Http.Json.JsonOptions>(opt =>
{
    opt.SerializerOptions.Converters.Add(new JsonStringEnumConverter());
});

If you are using Aspnet Core MVC with the minimal API use this:

        services.Configure<Microsoft.AspNetCore.Mvc.JsonOptions>(o => o.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter()));