title: Add-Migration not adding column to existing table in Entity Framework Core
body: <p>I am trying to add a new column to my existing table in database, i am specifying new field into class and running Add-Migration command but everytime it is creating a migration class for whole table with CreateTable method instead of AddColumn. Below is the class and generated migration class codes.</p>
  
  <pre><code>public class UserSetup
      {
          public int Id { get; set; }
          public string Name { get; set; }
          public bool Age{ get; set; } // New Field Added
  
      }
  </code></pre>
  
  <p>But for new field it is creating migration class for full table as shown below:</p>
  
  <pre><code>public partial class AddUserSetup_1 : Migration
      {
          protected override void Up(MigrationBuilder migrationBuilder)
          {
              migrationBuilder.CreateTable(
                  name: "UserSetup",
                  columns: table =&gt; new
                  {
                      Id = table.Column&lt;int&gt;(nullable: false)
                          .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                      Name= table.Column&lt;string&gt;(nullable: false),
                      Age= table.Column&lt;int&gt;(nullable: false),
                   },
                  constraints: table =&gt;
                  {
                      table.PrimaryKey("PK_UserSetup", x =&gt; x.Id);
                  });
  
         }
  
          protected override void Down(MigrationBuilder migrationBuilder)
          {
              migrationBuilder.DropTable(
                  name: "UserSetup");
          }
      }
  </code></pre>
  
  <p>Also in Add-Migration it is giving me the following error but even migration class is getting created.</p>
  
  <p><strong>System.UnauthorizedAccessException: Access to the path 'C:\Projects\PSM\Portal\src\Portal\Migrations\ApplicationDbContextModelSnapshot.cs' is denied.</strong> </p>