Entity Framework Core でテーブル作成時に "The entity type '(レコードオブジェクト)' requires a primary key to be defined." エラーが発生しテーブルが作成されない - C#

現象

System.InvalidOperationException
  HResult=0x80131509
  Message=The entity type '(テーブルのレコードオブジェクト)' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types, see https://go.microsoft.com/fwlink/?linkid=2141943.
  Source=Microsoft.EntityFrameworkCore

再現プログラム例

UI

コード

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EntityFrameworkCoreCreateTableSqlServer
{
  public class MyTable1Rec
  {
    public int id;
    public string Name;
    public string Category;
    public string Code;
    public int Price;
  }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;

namespace EntityFrameworkCoreCreateTableSqlServer
{
  public class MyDbContext : DbContext
  {
    public DbSet<MyTable1Rec> MyTable1 { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
    {
      options.UseSqlServer("Data Source=(DBホスト名またはIPアドレス);Initial Catalog=iPentecSandBox3;User ID=(ユーザーID);Password=(パスワード);Encrypt=False");
    }
  }
}

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Storage;

namespace EntityFrameworkCoreCreateTableSqlServer
{
  public partial class Form1 : Form
  {
    public Form1()
    {
      InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
      MyDbContext mc = new MyDbContext();
      RelationalDatabaseCreator rdc = (RelationalDatabaseCreator)mc.Database.GetService<IDatabaseCreator>();
      rdc.CreateTables();

      textBox1.Text += "テーブルを作成しました。\r\n";
    }
  }
}

実行結果

System.InvalidOperationException
  HResult=0x80131509
  Message=The entity type 'MyTable1Rec' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types, see https://go.microsoft.com/fwlink/?linkid=2141943.
  Source=Microsoft.EntityFrameworkCore

原因

対処法

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EntityFrameworkCoreCreateTableSqlServer
{
  public class MyTable1Rec
  {
    public int id { get; set; }
    public string Name { get; set; }
    public string Category { get; set; }
    public string Code { get; set; }
    public int Price { get; set; }
  }
}

著者

Penta

iPentecのメインプログラマー
C#, ASP.NET の開発がメイン、少し前まではDelphiを愛用