title: play 2.0 how to define a finder with multiple keys
body: <p>Assume that there is a Model bean with a unique contraint combining two columns (as composite primary keys) like this:</p>
  
  <pre><code>@Entity
  @Table(uniqueConstraints = {  @UniqueConstraint(columnNames = { "key1", "key2" }) })
  public class Rating extends Model {
  
      @ManyToOne
      @JoinColumn(name="key1", nullable=false)
      public Post key1;
  
      @ManyToOne
      @JoinColumn(name="key2", nullable=false)
      public User key2;
      ...
  }
  </code></pre>
  
  <p>How can i find a finder for the method with the following signature:</p>
  
  <pre><code>public static Rating get(Post key1, User key2) { ... }
  </code></pre>