ASP.NET MVC Core API Serialize Enums to String

Question

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'

Solution 1

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()));

Solution 2

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

Comments

[Tobias]

If you have a Web API then instead of .AddMvc() you can also use services.AddControllers().AddJsonOptions(...).

[Sudhanshu Mishra]

as of asp.net core 3.1 and Microsoft.AspNetCore.Mvc.NewtonsoftJson 3.1.5, there is a slight change: <pre> services.AddControllers() .AddNewtonsoftJson(opts => opts.SerializerSettings.Converters.Add(new StringEnumConverter())); </pre>

[drowhunter]

what if i dont want to do this accross the bard ? is there a way to do this as an attribute on my dto?

[ashlar64]

I found this website to be very helpful: jasongaylord.com/blog/2020/07/17/…

[Gavin]

@drowhunter If you want to just do this or a specific property, you can simply annotate the property in the return DTO like this [JsonConverter(typeof(JsonStringEnumConverter))] public CategoryDto Category { get; set; }. You will need to import the using System.Text.Json.Serialization namespace

[Qwerty]

Thank you this worked for me services.AddControllers()..AddJsonOptions(opts => { opts.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter()); })