sokil / php-mongo

                $this->operator->set($fieldName, $value);

            }

        } // field exists and is array

        else {

            if ($this->getId()) {

                $setValue = $this->operator->get('$set', $fieldName);

                if ($setValue) {

                    $setValue[] = $value;

                    $this->operator->set($fieldName, $setValue);

                } else {

                    $this->operator->push($fieldName, $value);

                }

            }

            $value = array_merge($oldValue, array($value));

        }

        // update local data

        parent::set($fieldName, $value);

            // check if old value is list or sub document

            // on sub document throw exception

            throw new InvalidOperationException(sprintf('The field "%s" must be an array but is of type Object', $fieldName));

        } else {

            // check if already in set

            if (in_array($value, $set)) {

                return $this;

            }

            $updatedSet = array_merge($set, array($value));

            if ($this->getId()) {

                $setValue = $this->operator->get('$set', $fieldName);

                if ($setValue) {

                    $this->operator->set($fieldName, $updatedSet);

                } else {

                    $this->operator->addToSet($fieldName, $value);

                }

            }

        }

        parent::set($fieldName, $updatedSet);