public function save()
        {
            $query = [];

            // remove any expression fields as they are already baked into the query
            $values = array_values(array_diff_key($this->_dirty_fields, $this->_expr_fields));

            if (!$this->_is_new) { // UPDATE
                // If there are no dirty values, do nothing
                if (empty($values) && empty($this->_expr_fields)) {
                    return true;
                }

                $query = $this->_buildUpdate();
                $id = $this->id(true);

                if (Arrays::is($id)) {
                    $values = array_merge($values, array_values($id));
                } else {
                    $values[] = $id;
                }
            } else { // INSERT
                $query = $this->_buildInsert();
            }

            $success = self::_execute($query, $values, $this->_connection_name);
            $caching_auto_clear_enabled = self::$_config[$this->_connection_name]['caching_auto_clear'];

            if ($caching_auto_clear_enabled){
                self::clear_cache($this->_table_name, $this->_connection_name);
            }

            // If we've just inserted a new record, set the ID of this object
            if ($this->_is_new) {
                $this->_is_new = false;

                if ($this->count_null_id_columns() != 0) {
                    $db = self::get_db($this->_connection_name);

                    if($db->getAttribute(PDO::ATTR_DRIVER_NAME) == 'pgsql') {
                        // it may return several columns if a compound primary
                        // key is used
                        $row = self::get_last_statement()->fetch(PDO::FETCH_ASSOC);

                        foreach($row as $key => $value) {
                            $this->_data[$key] = $value;
                        }
                    } else {
                        $column = $this->_getIdColumnName();
                        // if the primary key is compound, assign the last inserted id
                        // to the first column

                        if (Arrays::is($column)) {
                            $column = array_slice($column, 0, 1);
                        }

                        $this->_data[$column] = $db->lastInsertId();
                    }
                }
            }

            $this->_dirty_fields = $this->_expr_fields = [];

            return $success;
        }