csharpessentials-aspnetcore

name	csharpessentials-aspnetcore
description	Use when wiring CSharpEssentials Result<T> into ASP.NET Core — GlobalExceptionHandler maps unhandled exceptions to ProblemDetails, ResultEndpointFilter converts Result<T> returns to HTTP responses, and ConfigureSwaggerOptions adds per-version Swagger docs.

CSharpEssentials.AspNetCore

ASP.NET Core integration for functional patterns: error-to-ProblemDetails mapping and automatic Result-to-HTTP conversion.

Installation

dotnet add package CSharpEssentials.AspNetCore

Namespace

using CSharpEssentials.AspNetCore;

---

GlobalExceptionHandler + ProblemDetails

Catches unhandled exceptions and converts them to RFC 9457 ProblemDetails responses using ErrorType → HTTP status mapping.

// Program.cs
builder.Services.AddExceptionHandler<GlobalExceptionHandler>();
builder.Services.AddProblemDetails();

app.UseExceptionHandler();

// ErrorType → HTTP status mapping:
// Validation    → 400
// Unauthorized  → 401
// Forbidden     → 403
// NotFound      → 404
// Conflict      → 409
// Failure       → 422
// Unexpected    → 500

---

ResultEndpointFilter

Converts Result<T> returns from minimal API handlers into HTTP responses automatically.

// Apply to a group
app.MapGroup("/api").AddEndpointFilter<ResultEndpointFilter>();

// Handler just returns Result<T>
app.MapGet("/users/{id}", async (Guid id, UserService svc) =>
    await svc.GetUserAsync(id));   // returns Result<User>

// IsSuccess  → 200 OK with JSON body
// IsFailure  → ProblemDetails with status from ErrorType

Custom error mapping:

public class MyErrorMapper : IResultErrorMapper
{
    public int MapToStatusCode(ErrorType errorType) => errorType switch
    {
        ErrorType.NotFound   => 404,
        ErrorType.Validation => 422,
        _                    => 500
    };
}

builder.Services.AddSingleton<IResultErrorMapper, MyErrorMapper>();

---

API Versioning + Swagger

builder.Services.AddApiVersioning(options =>
{
    options.DefaultApiVersion = new ApiVersion(1);
    options.ReportApiVersions = true;
})
.AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV";
    options.SubstituteApiVersionInUrl = true;
});

builder.Services.ConfigureOptions<ConfigureSwaggerOptions>();
builder.Services.AddSwaggerGen();

app.UseSwagger();
app.UseSwaggerUI(options =>
{
    foreach (var desc in app.DescribeApiVersions())
        options.SwaggerEndpoint($"/swagger/{desc.GroupName}/swagger.json", desc.GroupName);
});

---

Best Practices

• Register GlobalExceptionHandler before AddProblemDetails
• Apply ResultEndpointFilter at the group level, not per-endpoint
• error.Description is the field name — not error.Message