title: Solr filtering multiple children in nested documents
body: <p>I couldn't find out how to filter out only the relevant children in nested documents and returning them along with the parents, something like:</p>
  
  <p><em>Return all parents which have child documents with attribute1=value1 and attribute1=value2 and return only those children with the parent</em>.</p>
  
  <p>The structure of <em>one</em> document looks like this:</p>
  
  <pre><code>{
   category: parent,
   attr1: a,
   attr2: b,
     _childDocuments_ : [
     {
          category:child,
          childAttr1: x,
          // many more
     },
     {
          category:child,
          childAttr1: y,
          // many more
     }, 
     {
     // more children but should not be returned
     }]
  }
  </code></pre>
  
  <p>Using the child transformer all the children are returned. Using multiple childFilters inside the <code>[child]</code> transformer has no effect (first one is taken second, one is ignored).</p>
  
  <p>An example query would be</p>
  
  <pre><code>query='+attr1:(*)+{!parent which=category:parent}childAttr1:x 
         +{!parent which=category:parent}childAttr1:y', 
         'fl':'*,[child parentFilter=category:parent childFilter=childAttr1:x11]'
  </code></pre>
  
  <p>I am using the JSON API for querying, grouping the result by a parent attribute and filtering on some parent attributes, but that shouldn't matter (imho).</p>
  
  <p>Thanks a lot for your time and I hope the question is well written.</p>