How to make enum serialization default to string in minimal API endpoints and Swagger?

Question

I'm working with .NET minimal APIs and have encountered a problem with JSON serialization/deserialization behavior for enums. Despite my attempts to change the behavior to use strings instead of integers, Swashbuckle.AspNetCore's Swagger documentation continues to represent enums as integers.

using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);

// Docs: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/minimal-apis?view=aspnetcore-7.0#configure-json-deserialization-options-globally
builder.Services.ConfigureHttpJsonOptions(options =>
{
    options.SerializerOptions.Converters.Add(new JsonStringEnumConverter());
});

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.MapPost("/api/v1/test", (TestRequest request) => Results.Ok(request));

app.Run();

public enum GridType
{
    Arithmetic,
    Geometric
}

public class TestRequest
{
    public required string Name { get; init; }
    public required GridType Type { get; set; }
}

But when Swagger UI opens, I still get an integer for the enum:

{
  "name": "string",
  "type": 0
}

The expected output is:

{
  "name": "string",
  "type": "Arithmetic"
}

@GuruStron, hey, just edited my question with a minimal reproducible example. — nop
– nop, Commented Jul 8, 2023 at 16:54

Guru Stron · Accepted Answer · 2023-07-08 23:47:11Z

37

There is an issue between MinimalApi and Swashbuckle Swagger you have to set the option in two different places:

builder.Services.ConfigureHttpJsonOptions(options =>
{
    options.SerializerOptions.Converters.Add(new JsonStringEnumConverter());
});
builder.Services.Configure<Microsoft.AspNetCore.Mvc.JsonOptions>(options =>
{
    options.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
});

More info about the issue: https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/2293

edited Jul 8, 2023 at 23:47

Guru Stron

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answered Jul 8, 2023 at 17:11

ctyar

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4 Comments

Guru Stron Over a year ago

Updated the code. The new (available since .NET 7) ConfigureHttpJsonOptions method allows to skip the namespace.

nop Over a year ago

Ohh, so that's why. Thanks

Alex Klaus Over a year ago

The reason why there's a need in Mvc.Json: "Swashbuckle.AspNetCore 6.x picks up changes from Microsoft.AspNetCore.Mvc.JsonOptions options. However, minimal API uses Microsoft.AspNetCore.Http.Json.JsonOptions. Therefore, both of them need to be configured so that Swagger schemas match the API output."

Gaspa79 Jun 17 at 16:11

Finally! Thank you

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