title: Ad-Hoc Validation is not executed
body: <p>I have a simple entity called <code>Game</code>. I want to allow my users to edit multiple of these entities at once. Therefore I need a form that contains multiple <code>Game</code> Entities.</p>
  
  <p>The problem: When the form is submitted and I invoke <code>hasErrors()</code> my custom ad-hoc <code>validate</code> method in the <code>Game</code> entities is never called. Only the validations marked by annotations are checked and produce errors when they are invalid.</p>
  
  <p>This is the <code>Game</code> Entity:</p>
  
  <pre><code>@Entity 
  public class Game extends Model {
      @Id
      public Long id;
  
      @ManyToOne
      @Constraints.Required
      public Team team1;
  
      @ManyToOne
      @Constraints.Required
      public Team team2;
  
      //the validate method does not get called
      public String validate()
      {
          System.out.println("Validating the Game Entity.");
          if(team1.id == team2.id)
              return "You have to choose two different teams!";
  
          return null;
      }    
  
      public static Model.Finder&lt;Long,Game&gt; find = new Model.Finder&lt;Long,Game&gt;(Long.class, Game.class);
  }
  </code></pre>
  
  <p>This is the Form that contains multiple <code>Game</code> Entities.</p>
  
  <pre><code>public class GameForm {
  
      @Valid
      public List&lt;Game&gt; games;
  
      public GameForm()
      {
          games = new ArrayList&lt;Game&gt;();
      }   
  }
  </code></pre>
  
  <p>This is the controller method.</p>
  
  <pre><code>public static Result save()
  {
      Form&lt;GameForm&gt; gameForm = form(GameForm.class).bindFromRequest();
  
      if(gameForm.hasErrors())
          return badRequest(create.render(gameForm));
  
      return redirect(
          routes.Games.index()
      );
  }
  </code></pre>