title: Sonata Admin Collection with sort and delete
body: <p>I'm trying to use a <code>sonata_type_collection</code> field for a list of ingredients associated to recipes.  Running into two issues:</p>
  
  <ol>
  <li><p>The sortable parameter works for drag/drop re-ordering, but I can't get the items in
  the association to actually sort by that column.</p></li>
  <li><p>The delete checkbox isn't working for deleting the associations.</p></li>
  </ol>
  
  <p>The association is a <code>ManyToOne</code>, because the reference table has more data than just a simple reference to the Recipe table, otherwise I'd use a <code>ManyToMany</code>.</p>
  
  <p>The <code>sortable</code> parameter worked nicely, making the rows draggable, however the list of ingredients isn't <em>sorted</em> by that column.  So although it saves the <code>position</code> column as it should, it doesn't actually display them in that order.</p>
  
  <p>I tried to find a simple way to hook into the <code>PersistentCollection</code> in order to filter it.  I found the <code>matching()</code> function which works, but it doesn't modify the underlying collection, it just retuns back an <code>ArrayCollection</code>.  That doesn't work because I can't replace the <code>PersistentCollection</code> with an <code>ArrayCollection</code>.</p>
  
  <p>Also the delete function didn't work out of the box.  I had to manually override <code>RecipeAdmin::preUpdate($object)</code> and manually remove the deleted ingredients and flush the Entity Manager.</p>
  
  <p>I feel like there should be a much simpler way to do all this.</p>
  
  <p>UPDATE: I discovered the <code>@OrderBy</code> annotation today which solves the sorting issue</p>