Why should you care?

Stable JSON contracts let mobile and web clients evolve independently from database schema.

See it live — copy this example

Create a Web API project (dotnet new webapi), paste the code, then run dotnet run.

public static class UserEndpoints
{
    public static void MapUserEndpoints(this WebApplication app)
    {
        app.MapPost("/users", async (RegisterUserRequest req, RegisterUserHandler h, CancellationToken ct) =>
        {
            var id = await h.HandleAsync(new RegisterUserCommand(req.Name, req.Email), ct);
            return Results.Created($"/users/{id}", new { id });
        });
        app.MapGet("/users/{id:guid}", async (Guid id, GetUserHandler h, CancellationToken ct) =>
        {
            var dto = await h.HandleAsync(id, ct);
            return dto is null ? Results.NotFound() : Results.Ok(dto);
        });
    }
}

Run Example »

Edit the code and click Run — like W3Schools Try it Yourself.

What happened?

• RegisterUserRequest is API DTO.
• Handler returns id or UserDto.
• CreatedAtRoute pattern gives REST-friendly responses.

Try it yourself

1. Map POST /users and GET /users/{id}.
2. Test in Swagger with valid and invalid email.
3. Verify ShopNest_Users table in SSMS.
4. Change a string or route in the example and save — watch Swagger or the RabbitMQ Management UI update.
5. Break the code on purpose (remove a semicolon), read the error message, then fix it.

Remember

API maps HTTP → handlers. DTOs at the boundary. User service complete — template for Product service.