CI框架源碼閱讀---------DB.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP 5.1.6 or newer
 *
 * @package		CodeIgniter
 * @author		ExpressionEngine Dev Team
 * @copyright	Copyright (c) 2008 - 2011, EllisLab, Inc.
 * @license		http://codeigniter.com/user_guide/license.html
 * @link		http://codeigniter.com
 * @since		Version 1.0
 * @filesource
 */

// ------------------------------------------------------------------------

/**
 * Initialize the database
 * 初始化數據庫類 
 *
 * @category	Database
 * @author		ExpressionEngine Dev Team
 * @link		http://codeigniter.com/user_guide/database/
 * @param 	string
 * @param 	bool	Determines if active record should be used or not
 */
function &DB($params = '', $active_record_override = NULL)
{
	// Load the DB config file if a DSN string wasn't passed
	// 如果沒有傳遞過來DSN參數的話，載入DB配置文件
	if (is_string($params) AND strpos($params, '://') === FALSE)
	{
		// Is the config file in the environment folder?
		// 是否配置文件在配置的環境文件夾中
		if ( ! defined('ENVIRONMENT') OR ! file_exists($file_path = APPPATH.'config/'.ENVIRONMENT.'/database.php'))
		{
			// 如果環境變量中沒有database.php 則報錯
			if ( ! file_exists($file_path = APPPATH.'config/database.php'))
			{
				show_error('The configuration file database.php does not exist.');
			}
		}

		include($file_path);

		// 不存在數據庫的配置
		if ( ! isset($db) OR count($db) == 0)
		{
			show_error('No database connection settings were found in the database config file.');
		}

		if ($params != '')
		{
			$active_group = $params;
		}

		if ( ! isset($active_group) OR ! isset($db[$active_group]))
		{
			show_error('You have specified an invalid database connection group.');
		}

		$params = $db[$active_group];
	}
	elseif (is_string($params))
	{

		/*  parse the URL from the DSN string
		 *  使用parse_url解析DSN
		 *  Database settings can be passed as discreet
		 *  parameters or as a data source name in the first
		 *  數據庫配置可以作爲參數或者是在第一個參數中作爲數據源名稱傳遞過來
		 *  parameter. DSNs must have this prototype:
		 *  DSN必須有這個原型：
		 *  $dsn = 'driver://username:password@hostname/database';
		 */
		
		// parse_url() 解析 URL，返回其組成部分
		if (($dns = @parse_url($params)) === FALSE)
		{
			show_error('Invalid DB Connection String');
		}

		// rawurldecode()已編碼的 URL 字符串進行解碼
		$params = array(
							'dbdriver'	=> $dns['scheme'],
							'hostname'	=> (isset($dns['host'])) ? rawurldecode($dns['host']) : '',
							'username'	=> (isset($dns['user'])) ? rawurldecode($dns['user']) : '',
							'password'	=> (isset($dns['pass'])) ? rawurldecode($dns['pass']) : '',
							'database'	=> (isset($dns['path'])) ? rawurldecode(substr($dns['path'], 1)) : ''
						);


		// were additional config items set?
		// 是否設置了額外的配置項
		if (isset($dns['query']))
		{
			// parse_str()解析查詢字符串到變量中
			parse_str($dns['query'], $extra);

			foreach ($extra as $key => $val)
			{
				// booleans please
				// 把字符串轉換true，false轉換爲真正boolean值
				if (strtoupper($val) == "TRUE")
				{
					$val = TRUE;
				}
				elseif (strtoupper($val) == "FALSE")
				{
					$val = FALSE;
				}

				$params[$key] = $val;
			}
		}
	}

	// No DB specified yet?  Beat them senseless...
	// 沒有指定要連接的數據庫驅動
	if ( ! isset($params['dbdriver']) OR $params['dbdriver'] == '')
	{
		show_error('You have not selected a database type to connect to.');
	}

	// Load the DB classes.  Note: Since the active record class is optional
	// we need to dynamically create a class that extends proper parent class
	// based on whether we're using the active record class or not.
	// Kudos to Paul for discovering this clever use of eval()
	// 載入DB類。 注意： 因爲active record類是可選的，我們需要動態的去
	// 創建一個繼承適當的父類（基於我們是否使用active record類）

	if ($active_record_override !== NULL)
	{
		$active_record = $active_record_override;
	}

	require_once(BASEPATH.'database/DB_driver.php');

	// 啓用active_record
	if ( ! isset($active_record) OR $active_record == TRUE)
	{
		require_once(BASEPATH.'database/DB_active_rec.php');

		// 動態創建CI_DB類繼承自CI_DB_active_record類
		if ( ! class_exists('CI_DB'))
		{
			eval('class CI_DB extends CI_DB_active_record { }');
		}
	}
	else
	{
		// 動態創建CI_DB直接繼承自CI_DB_driver
		if ( ! class_exists('CI_DB'))
		{
			eval('class CI_DB extends CI_DB_driver { }');
		}
	}

	// 加載響應的數據庫驅動
	require_once(BASEPATH.'database/drivers/'.$params['dbdriver'].'/'.$params['dbdriver'].'_driver.php');

	// Instantiate the DB adapter
	// 實例化DB適配器
	$driver = 'CI_DB_'.$params['dbdriver'].'_driver';
	$DB = new $driver($params);

	// 在DB_driver中的字段，用於指定是否要對數據庫驅動進行初始化操作
	if ($DB->autoinit == TRUE)
	{
		$DB->initialize();
	}

	if (isset($params['stricton']) && $params['stricton'] == TRUE)
	{
		$DB->query('SET SESSION sql_mode="STRICT_ALL_TABLES"');
	}

	return $DB;
}



/* End of file DB.php */
/* Location: ./system/database/DB.php */