title: How to do a join in Elasticsearch -- or at the Lucene level
body: <p>What's the best way to do the equivalent of an SQL join in Elasticsearch?</p>
  
  <p>I have an SQL setup with two large tables: Persons and Items. 
  A Person can own <em>many</em> items.
  Both Person and Item rows can change (i.e. be updated).
  I have to run searches which filter by aspects of both the person and the item.</p>
  
  <p>In Elasticsearch, it looks like you could make Person a nested document of Item, then use <code>has_child</code>.</p>
  
  <p>But: if you then update a Person, I think you'd need to update every Item they own (which could be a lot).</p>
  
  <p>Is that correct?
  Is there a nice way to solve this query in Elasticsearch?</p>