/**
  * Add diff between stage post and production post.
  *
  * @param Post_Env_Diff $diff
  */
 private function add_post_diff(Post_Env_Diff $diff)
 {
     // Store diff if it does not already exist.
     if (!isset($this->post_diffs[$diff->get_stage_id()])) {
         // Store diff in database.
         add_post_meta($this->batch->get_id(), 'sme_post_diff', $diff->to_array());
         // Store diff in property.
         $this->post_diffs[$diff->get_stage_id()] = $diff;
     }
 }
 /**
  * Get post environment diff object for a batch.
  *
  * @param Batch $batch
  *
  * @return array
  */
 public function get_post_diffs(Batch $batch)
 {
     $objects = array();
     $diffs = get_post_meta($batch->get_id(), 'sme_post_diff');
     if (empty($diffs)) {
         return $objects;
     }
     foreach ($diffs as $diff) {
         $obj = new Post_Env_Diff($diff['stage_id']);
         $obj->set_revision_id($diff['revision_id']);
         $obj->set_prod_id($diff['prod_id']);
         $obj->set_stage_status($diff['stage_status']);
         $obj->set_parent_guid($diff['parent_guid']);
         $objects[$diff['stage_id']] = $obj;
     }
     return $objects;
 }