title: QueryDsl - filtering Map based on key
body: <p>I have folowing property in my hibenrate entity class:</p>
  
  <pre><code>@MapKeyJoinColumn(name = "language_code")
  @LazyCollection(LazyCollectionOption.EXTRA)
  @ElementCollection(fetch = FetchType.LAZY)
  @CollectionTable(name = "text_translations", joinColumns = @JoinColumn(name = "text_id"))
  private Map&lt;Language, String&gt; translations = new HashMap&lt;&gt;();
  </code></pre>
  
  <p>Now I want to query this entity and filter content of map by user's language (i.e. by map's key). I have folowing join in my query:</p>
  
  <pre><code>StringPath titleTran = new StringPath("title_tran");
  from(entity).
  .leftJoin(entity.translations, titleTran).fetch().where(?mapKey?.eq(userLanguage));
  </code></pre>
  
  <p>What I need is ?mapKey? to by path to language of titleTran path. Is this somehow possible in QueryDsl?</p>