EF Core 2.0 Cannot specify primary key for model

It could very well be trivial, but I can't see what's missing in the following snippet:

using System;
using System.ComponentModel.DataAnnotations;

namespace Intro.Models {
    public class Todo {
        [Key, Required]
        public Int32 Id;
        public String Name;
        public String Note;
        public DateTime Created;
        public Boolean Completed;
    }
}

I've also tried 

Int32 ID;

The entity type 'Todo' requires a primary key to be defined.
   at Microsoft.VisualStudio.Web.CodeGeneration.ActionInvoker.<BuildCommandLine>b__6_0()
   at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args)
   at Microsoft.VisualStudio.Web.CodeGeneration.ActionInvoker.Execute(String[] args)
   at Microsoft.VisualStudio.Web.CodeGeneration.CodeGenCommand.Execute(String[] args)

I am trying to follow an outdated 1.1 tutorial on Microsoft Docs, and was trying to scaffold some views/controllers with:

dotnet aspnet-codegenerator controller -name TodoController-m Todo-dc TodoContext--relativeFolderPath Controllers--useDefaultLayout --referenceScriptLibraries

My 

DbContext

using System;
using Microsoft.EntityFrameworkCore;

namespace Intro.Models{publicclassTodoContext:DbContext{publicTodoContext(DbContextOptions<TodoContext> options):base(options){}publicDbSet<Todo>Todos{ get;set;}//protected override void OnModelCreating(ModelBuilder modelBuilder) {//    modelBuilder.Entity<Todo>().HasKey(todo => todo.Id);//}}}

And my 

Startup

using Microsoft.EntityFrameworkCore;
using Intro.Models;

namespace Intro{publicclassStartup{publicIConfigurationConfiguration{ get;}publicStartup(IConfiguration configuration){Configuration= configuration;}publicvoidConfigureServices(IServiceCollection services){// MVC stuff deducted   
            services.AddDbContext<TodoContext>(options => options.UseSqlServer("Server=127.0.0.1;Database=LearnCSharp.Intro.Test1;User Id=SA;Password=smallC!0ud;"));}// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.publicvoidConfigure(IApplicationBuilder app,IHostingEnvironment env){// MVC stuff deducted...// Ensure createdvar context =newTodoContext(app.ApplicationServices.GetRequiredService<DbContextOptions<TodoContext>>());
            context.Database.EnsureCreated();}}}

Finally my 

BuildWebHost()

returnWebHost.CreateDefaultBuilder(args).UseApplicationInsights().UseStartup<Startup>().UseDefaultServiceProvider(options => options.ValidateScopes=false).Build();

I read