title: Using java driver to match only if array contains a value equal to another embedded field
body: <p>I am a beginner at MongoDB. In a pipeline my collection contains documents:</p>
  <pre><code>Document{{_id=1, AnyLikes=[2, 3, 4], ILikes=Document{{_id=2}}, TwoLikes=Document{{_id=1}}}}
  Document{{_id=1, AnyLikes=[2, 3, 4], ILikes=Document{{_id=2}}, TwoLikes=Document{{_id=3}}}}
  Document{{_id=1, AnyLikes=[2, 3, 4], ILikes=Document{{_id=2}}, TwoLikes=Document{{_id=4}}}}
  </code></pre>
  <p>I want to filter only those where AnyLikes contains an element equal to the _id of the TwoLikes document.  So for the above it should return only the second and third documents.
  I tried:</p>
  <pre><code>persons.aggregate(asList(match(elemMatch(&quot;AnyLikes&quot;, eq(&quot;$TwoLikes._id&quot;)))));
  </code></pre>
  <p>Any idea why it is not working?  I get no results.</p>