title: Room @Relation with composite Primary Key
body: <p>my question is an extension of this question (also mine :) ) -> <a href="https://stackoverflow.com/questions/50248668/room-composite-primary-key-link-to-foreign-key">Room composite Primary Key link to Foreign Key</a>
  So, if I have this class:</p>
  
  <pre><code>public class FoodWithIngredients extends Food{
  
      @Relation(parentColumn = "id", entityColumn = "food_id", entity = 
      Ingredient.class)
      private List&lt;Ingredient&gt; mIngredients;
  
  }
  </code></pre>
  
  <p>But the <code>PrimaryKey</code> of "Food" table is <code>composite</code> <code>(primaryKeys = {"id", "language_id"})</code>.</p>
  
  <p>How I can make the @Relation returns records where <code>"parentColumn = {"id", "language_id"}, entityColumn = {"food_id", food_language_id}"</code> ?</p>