title: InvalidOperationException: Cannot create a DbSet for 'Role' because this type is not included in the model for the context
body: <p>The following solution works in .net core 1.1, but after upgrading from 1.1 to 2.0, I received the following error:</p>
  
  <blockquote>
    <p>InvalidOperationException: Cannot create a DbSet for 'Role' because this type is not included in the model for the context.</p>
  </blockquote>
  
  <p>When the user attempts to log in and the following statement is executed:</p>
  
  <pre><code>var result = await _signInManager.PasswordSignInAsync(model.Email, 
                                  model.Password, model.RememberMe, lockoutOnFailure: false);
  </code></pre>
  
  <p>What is wrong?</p>
  
  <hr>
  
  <p><strong>User.cs</strong></p>
  
  <pre><code>public partial class User : IdentityUser&lt;Guid&gt;
  {
      public string Name { get; set; }
  }
  </code></pre>
  
  <p><strong>IdentityEntities.cs</strong></p>
  
  <pre><code>public partial class UserLogin : IdentityUserLogin&lt;Guid&gt;
  {
  }
  public partial class UserRole : IdentityUserRole&lt;Guid&gt;
  {
  }
  public partial class UserClaim : IdentityUserClaim&lt;Guid&gt;
  {
  }
  public partial class Role : IdentityRole&lt;Guid&gt;
  {
      public Role() : base()
      { 
      }
  
      public Role(string roleName)
      {
          Name = roleName;
      }
  }
  public partial class RoleClaim : IdentityRoleClaim&lt;Guid&gt;
  {
  }
  public partial class UserToken : IdentityUserToken&lt;Guid&gt;
  {
  }
  </code></pre>
  
  <p><strong>ConfigureServices</strong></p>
  
  <pre><code>services.AddIdentity&lt;User, Role&gt; 
  </code></pre>