CI_DB_driver::query PHP Method

    public function query($sql, $binds = FALSE, $return_object = NULL)
    {
        if ($sql === '') {
            log_message('error', 'Invalid query: ' . $sql);
            return $this->db_debug ? $this->display_error('db_invalid_query') : FALSE;
        } elseif (!is_bool($return_object)) {
            $return_object = !$this->is_write_type($sql);
        }
        // Verify table prefix and replace if necessary
        if ($this->dbprefix !== '' && $this->swap_pre !== '' && $this->dbprefix !== $this->swap_pre) {
            $sql = preg_replace('/(\\W)' . $this->swap_pre . '(\\S+?)/', '\\1' . $this->dbprefix . '\\2', $sql);
        }
        // Compile binds if needed
        if ($binds !== FALSE) {
            $sql = $this->compile_binds($sql, $binds);
        }
        // Is query caching enabled? If the query is a "read type"
        // we will load the caching class and return the previously
        // cached query if it exists
        if ($this->cache_on === TRUE && $return_object === TRUE && $this->_cache_init()) {
            $this->load_rdriver();
            if (FALSE !== ($cache = $this->CACHE->read($sql))) {
                return $cache;
            }
        }
        // Save the query for debugging
        if ($this->save_queries === TRUE) {
            $this->queries[] = $sql;
        }
        // Start the Query Timer
        $time_start = microtime(TRUE);
        // Run the Query
        if (FALSE === ($this->result_id = $this->simple_query($sql))) {
            if ($this->save_queries === TRUE) {
                $this->query_times[] = 0;
            }
            // This will trigger a rollback if transactions are being used
            if ($this->_trans_depth !== 0) {
                $this->_trans_status = FALSE;
            }
            // Grab the error now, as we might run some additional queries before displaying the error
            $error = $this->error();
            // Log errors
            log_message('error', 'Query error: ' . $error['message'] . ' - Invalid query: ' . $sql);
            if ($this->db_debug) {
                // We call this function in order to roll-back queries
                // if transactions are enabled. If we don't call this here
                // the error message will trigger an exit, causing the
                // transactions to remain in limbo.
                while ($this->_trans_depth !== 0) {
                    $trans_depth = $this->_trans_depth;
                    $this->trans_complete();
                    if ($trans_depth === $this->_trans_depth) {
                        log_message('error', 'Database: Failure during an automated transaction commit/rollback!');
                        break;
                    }
                }
                // Display errors
                return $this->display_error(array('Error Number: ' . $error['code'], $error['message'], $sql));
            }
            return FALSE;
        }
        // Stop and aggregate the query time results
        $time_end = microtime(TRUE);
        $this->benchmark += $time_end - $time_start;
        if ($this->save_queries === TRUE) {
            $this->query_times[] = $time_end - $time_start;
        }
        // Increment the query counter
        $this->query_count++;
        // Will we have a result object instantiated? If not - we'll simply return TRUE
        if ($return_object !== TRUE) {
            // If caching is enabled we'll auto-cleanup any existing files related to this particular URI
            if ($this->cache_on === TRUE && $this->cache_autodel === TRUE && $this->_cache_init()) {
                $this->CACHE->delete();
            }
            return TRUE;
        }
        // Load and instantiate the result driver
        $driver = $this->load_rdriver();
        $RES = new $driver($this);
        // Is query caching enabled? If so, we'll serialize the
        // result object and save it to a cache file.
        if ($this->cache_on === TRUE && $this->_cache_init()) {
            // We'll create a new instance of the result object
            // only without the platform specific driver since
            // we can't use it with cached data (the query result
            // resource ID won't be any good once we've cached the
            // result object, so we'll have to compile the data
            // and save it)
            $CR = new CI_DB_result($this);
            $CR->result_object = $RES->result_object();
            $CR->result_array = $RES->result_array();
            $CR->num_rows = $RES->num_rows();
            // Reset these since cached objects can not utilize resource IDs.
            $CR->conn_id = NULL;
            $CR->result_id = NULL;
            $this->CACHE->write($sql, $CR);
        }
        return $RES;
    }

 /**
  * @return Bitstream
  */
 public function get_original_bitstream()
 {
     $sql = "select a.bitstream_id as original_id, count(b.bitstream_id) as converted_count " . "from bitstream as a left join bitstream as b on a.bitstream_id = b.original_id " . "group by a.bitstream_id " . "having converted_count = 0 " . "and a.deleted = 0 " . "and a.type = 'uploaded'" . "order by a.bitstream_id desc limit 0,1";
     $query = $this->db->query($sql);
     //echo $query->num_rows();
     if ($query->num_rows() == 0) {
         return NULL;
     }
     $result = $query->result_array();
     if (!isset($result[0])) {
         return NULL;
     }
     //print_r($result);
     $bitstream_id = $result[0]["original_id"];
     $bitstream = new Bitstream($bitstream_id);
     // 再檢查一下
     $path = $bitstream->get_path();
     if (is_file($path) === FALSE) {
         $this->puli_log->create_log($bitstream, "delete");
         $bitstream->delete();
         return $this->get_original_bitstream();
     }
     return $bitstream;
 }