Vertical Slice all in one file example for creating a patient

CreatePatient.cs

namespace MyApp.UseCases.Patients.CreatePatient;

// 1. ENDPOINT
[ApiController]
public sealed class Endpoint(Handler handler) : ControllerBase
{
    [HttpPost("patients")]
    public async Task<ActionResult<Response>> Post(Request req, CancellationToken ct)
    {
        var res = await handler.HandleAsync(req, ct);
        return Created($"/patients/{res.PatientId}", res);
    }
}

// 2. CONTRACTS
public sealed record Request(string FirstName, string LastName, DateTime DateOfBirth, string Email);
public sealed record Response(int PatientId, string FullName, string Email);

// 3. VALIDATOR
public sealed class Validator : AbstractValidator<Request> 
{
    public Validator() { /* Rules... */ }
}

// 4. HANDLER
public sealed class Handler(HospitalDbContext db, IValidator<Request> validator)
{
    public async Task<Response> HandleAsync(Request req, CancellationToken ct)
    {
        await validator.ValidateAndThrowAsync(req, ct);

        // Map request -> entity
        var patient = new Patient { /* ... */ };

        // Save patient to database
        db.Patients.Add(patient);
        await db.SaveChangesAsync(ct);

        return new Response(
            patient.PatientId, 
            $"{patient.FirstName} {patient.LastName}", 
            patient.Email);
    }
}