title: Get children count via HQL
body: <p>I have a one-to-many mapping between a parent entity and child entities. Now I need to find the number of children associated with each parent for a list of parents. I am trying to do this with HQL but I am not sure how I can get the list of parents in there. Also, I don't know how I can return the entity itself and not just its ID. My current HQL query is:</p>
  
  <pre><code>select new map(parent.id as parentId, count(*) as childCount) 
  from Parent parent left join parent.children children
  group by parent.id
  </code></pre>
  
  <p>but this only returns the ID and does not filter on specific parents.</p>
  
  <p><strong>EDIT</strong>
  Based on Pascal's answer I have modified the query to </p>
  
  <pre><code>select new map(parent as parent, count(elements(parent.children)) as childCount) 
  from Parent parent
  group by parent
  </code></pre>
  
  <p>That does work, but is prohibitively slow: 30 seconds instead of 400 ms on the same database.</p>