Simplified ASP.NET Core app exploration

server.cs

#!/usr/bin/env dotnet run

var builder = WebApplication.CreateBuilder(args);
var config = builder.Configuration;
var connString = config["connectionString"] ?? "Data Source=todos.db";

builder.AddDbContext<TodoDb>(options => options.UseSqlite(connString));
builder.AddSqlite<Todo>(connString) // Higher level API perhaps?

var app = builder.Build();

// Step 0: Request delegate
app.MapGet("/", ctx => ctx.Respsone.WriteAsync("Hello, World!"));

// Step 1: Return string 
app.MapGet("/hello", () => "Hello, World!");

// Step 2: Return custom type
app.MapGet("/todo", () => new Todo("Do the thing"));

// Step 3: No DI
app.MapGet("/todo-db/{id}", async (int id) =>
{
    using var db = new TodoDb(connString);
    return await db.Todos.FindAsync(id) is Todo todo
        ? Ok(todo) : NotFound();
});

// Step 4: Use a DB
app.MapGet("/todo-db/{id}", async (int id, TodoDb db) =>
{
    return await db.Todos.FindAsync(id) is Todo todo
        ? Ok(todo) : NotFound();
});

app.MapPost("/todo-db", async (Todo todo, TodoDb db) =>
{
    db.Todos.Add(todo);
    await Todos.SaveChangesAsync();

    return Created(); // 204
    // return CreatedAt($"/todo-db/{todo.Id}", todo);
};

app.MapPut("/todo-db", async (int id, Todo inputTodo, TodoDb db) =>
{
    var todo = await db.Todos.FindAsync(id);

    if (todo is null) return NotFound();

    todo.Title = inputTodo.Title;
    todo.IsComplete = inputTodo.IsComplete;

    await db.SaveChanges();

    return NoContent();
});

app.MapDelete("/todo-db", async (int id, TodoDb db) =>
{
    if (await db.Todos.FindAsync(id) is Todo todo)
    {
        db.Todos.Remove(todo);
        await db.SaveChanges();
        return OK(todo);
    }

    return NotFound();
});

// Step 5: Input validation
app.MapPost("/todo-db", async (Validated<Todo> todo, TodoDb db) =>
{
    if (!todo.IsValid) return Problem(todo);

    db.Todos.Add(todo);
    await Todos.SaveChangesAsync();

    return CreatedAt($"/todo-db/{todo.InputObject.Id}", todo);
};

// Run app
await app.RunAsync();

// Data types
record Todo(string Title)
{
    public bool IsComplete { get; set; }
}

class TodoDb : DbContext
{
    private readonly string _cs;

    public TodoDb(string connectionString) : base() => _cs = connectionString; // Non-DI use scenario

    public TodoDb(DbContextOptions<TodoDb> options)
        : base(options)
    {

    }

    protected override OnConfiguring(DbContextOptionsBuilder optionsBuilder) // Non-DI use scenario
    {
        optionsBuilder.UseSqlite(_cs);
    }

    public DbSet<Todo> Todos { get; set; }
}

That's a scenario we're exploring but not actually confirmed for .NET 6 yet.