Program.cs

using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<TodoDb>(opt => opt.UseInMemoryDatabase("TodoList"));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddOpenApiDocument(config => {
    config.DocumentName = "TodoAPI";
    config.Title = "TodoAPI v1";
    config.Version = "v1";
});

var app = builder.Build();

if (app.Environment.IsDevelopment()) {
    app.UseOpenApi();
    app.UseSwaggerUi(config => {
        config.DocumentTitle = "TodoAPI";
        config.Path = "/swagger";
        config.DocumentPath = "/swagger/{documentName}/swagger.json";
        config.DocExpansion = "list";
    });
}

var todoItems = app.MapGroup("/todoitems");

todoItems.MapGet("/", async (TodoDb db) =>
    await db.Todos.ToListAsync());

todoItems.MapGet("/complete", async (TodoDb db) =>
    await db.Todos.Where(t => t.IsComplete).ToListAsync());

todoItems.MapGet("/{id}", async (int id, TodoDb db) =>
    await db.Todos.FindAsync(id)
        is Todo todo
            ? Results.Ok(todo)
            : Results.NotFound());

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

    return Results.Created($"/todoitems/{todo.Id}", todo);
});

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

    if (todo is null) return Results.NotFound();

    todo.Name = inputTodo.Name;
    todo.IsComplete = inputTodo.IsComplete;

    await db.SaveChangesAsync();

    return Results.NoContent();
});

todoItems.MapDelete("/{id}", async (int id, TodoDb db) =>
{
    if (await db.Todos.FindAsync(id) is Todo todo)
    {
        db.Todos.Remove(todo);
        await db.SaveChangesAsync();
        return Results.NoContent();
    }

    return Results.NotFound();
});

todoItems.MapPatch("/{id}", async (int id, TodoPatchDto inputTodo, TodoDb db) => {
    var todo = await db.Todos.FindAsync(id);

    if (todo is null) return Results.NotFound();

    if (inputTodo.Name is not null) todo.Name =  inputTodo.Name;
    if (inputTodo.IsComplete is not null) todo.IsComplete = inputTodo.IsComplete.Value;

    await db.SaveChangesAsync();
    return Results.NoContent();
});

app.Run();