Solución a bug al ordenar por entidad asociada.

Datagrid/Datagrid.php

@@ -113,7 +113,7 @@ class Datagrid implements DatagridInterface
         if (isset($this->values['_sort_by'])) {
             foreach ($this->getColumns()->getElements() as $fieldDescription){
                 if ($fieldDescription->isSortable() && $fieldDescription->getName() == $this->values['_sort_by']) {
-                    $this->query->setSortBy($fieldDescription->getParentAssociationMappings(), $fieldDescription->getSortFieldMapping());
+                    $this->query->setSortBy($fieldDescription->getSortParentAssociationMapping(), $fieldDescription->getSortFieldMapping());
                     $this->query->setSortOrder(isset($this->values['_sort_order']) ? $this->values['_sort_order'] : null);
 
                     break;