TT#30500 Fix /api/subscriberregistrations POST method

* POST method is adapted to the new behaviour of
      update_item() and fetch_item()

cherry-picked to mr5.5 (see TT#38607)

Change-Id: I35cc5d4e8c97cd415e9d6d31a6811d1f8cce84a9
(cherry picked from commit 53532fd5e8)

lib/NGCP/Panel/Controller/API/SubscriberRegistrations.pm

@@ -163,7 +163,9 @@ sub POST :Allow {
     my ($self, $c) = @_;
 
     {
-        my $resource = $self->get_valid_post_data(
+        my ($item, $resource);
+
+        $resource = $self->get_valid_post_data(
             c => $c,
             media_type => 'application/json',
         );
@@ -171,7 +173,17 @@ sub POST :Allow {
 
         my $form = $self->get_form($c);
         my $create = 1;
-        my $item = $self->update_item($c, undef, undef, $resource, $form, $create);
+
+        my ($guard, $txn_ok) = ($c->model('DB')->txn_scope_guard, 0);
+        {
+            $self->update_item($c, undef, undef, $resource, $form, $create);
+
+            $guard->commit;
+            $txn_ok = 1;
+        }
+        last unless $txn_ok;
+
+        $item = $self->fetch_item($c, $resource, $form, $item);
         last unless $item;
 
         $c->response->status(HTTP_CREATED);
@@ -187,5 +199,6 @@ sub end : Private {
     $self->log_response($c);
 }
 
+1;
 
 # vim: set tabstop=4 expandtab: