C# + .NET 7.0 - Serialize (Convert) Enum to String in API Response

Built with .NET 7.0

This is a quick post to show how to configure an ASP.NET Core API to serialize all enum properties to strings in HTTP responses.

By default enum properties are returned as a number, for example if you have the following enum for user roles:

 public enum Role { Admin, User }

A user with the Role = Role.Admin would be returned from the API as "role": 0, e.g:

 { "id": 1, "title": "Mr", "firstName": "George", "lastName": "Costanza", "email": "[email protected]", "role": 0 }

Convert Enums to Strings with JsonStringEnumConverter

To convert enums to strings in API responses so the above role would return the value "role": "Admin", add a call to .AddJsonOptions() after services.AddControllers() in the Program.cs file, and add a new JsonStringEnumConverter() to the JsonSerializerOptions.Converters list like the following.

 services.AddControllers().AddJsonOptions(x => { // serialize enums as strings in api responses (e.g. Role) x.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter()); });

Example .NET 7 Program.cs File

Below is a complete .NET 7 Program file that includes the above snippet to convert enums to strings. It's from a CRUD API tutorial I posted recently, the complete project and documentation is available at .NET 7.0 + Dapper + SQLite - CRUD API Tutorial in ASP.NET Core.

The Program file configures dependency injection, initializes a SQLite database, configures the HTTP request pipeline and starts the API.

 using System.Text.Json.Serialization; using WebApi.Helpers; using WebApi.Repositories; using WebApi.Services; var builder = WebApplication.CreateBuilder(args); // add services to DI container { var services = builder.Services; var env = builder.Environment; services.AddSingleton<DataContext>(); services.AddCors(); services.AddControllers().AddJsonOptions(x => { // serialize enums as strings in api responses (e.g. Role) x.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter()); // ignore omitted parameters on models to enable optional params (e.g. User update) x.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull; }); services.AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies()); // configure DI for application services services.AddScoped<IUserRepository, UserRepository>(); services.AddScoped<IUserService, UserService>(); } var app = builder.Build(); // ensure database and tables exist { using var scope = app.Services.CreateScope(); var context = scope.ServiceProvider.GetRequiredService<DataContext>(); await context.Init(); } // configure HTTP request pipeline { // global cors policy app.UseCors(x => x .AllowAnyOrigin() .AllowAnyMethod() .AllowAnyHeader()); // global error handler app.UseMiddleware<ErrorHandlerMiddleware>(); app.MapControllers(); } app.Run("http://localhost:4000");