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db.html
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<!DOCTYPE html>
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<div class='alert alert-success'>
我們開始分析database/DB.php。<br/>
DB共有三種載入方式。
</div>
<!-- You also need to add some content to highlight, but that is covered elsewhere. -->
<pre class="brush: php">
/**
* 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
*
* @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 = '', $active_record_override = NULL)
{
// Load the DB config file if a DSN string wasn't passed
if (is_string($params) AND strpos($params, '://') === FALSE)
{
// Is the config file in the environment folder?
if ( ! defined('ENVIRONMENT') OR ! file_exists($file_path = APPPATH.'config/'.ENVIRONMENT.'/database.php'))
{
if ( ! file_exists($file_path = APPPATH.'config/database.php'))
{
show_error('The configuration file database.php does not exist.');
}
}
include($file_path);
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];
</pre>
<div class='alert alert-success'>
第一種載入方式：若是$params為字串，並且不是Data Source Name，則前往config檔尋找資料庫設定值。
</div>
<pre class="brush: php">
}
elseif (is_string($params))
{
/* parse the URL from the DSN string
* Database settings can be passed as discreet
* parameters or as a data source name in the first
* parameter. DSNs must have this prototype:
* $dsn = 'driver://username:password@hostname/database';
*/
if (($dns = @parse_url($params)) === FALSE)
{
show_error('Invalid DB Connection String');
}
$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($dns['path'], 1)) : ''
);
// were additional config items set?
if (isset($dns['query']))
{
parse_str($dns['query'], $extra);
foreach ($extra as $key => $val)
{
// booleans please
if (strtoupper($val) == "TRUE")
{
$val = TRUE;
}
elseif (strtoupper($val) == "FALSE")
{
$val = FALSE;
}
$params[$key] = $val;
}
}
</pre>
<div class='alert alert-success'>
第二種載入方式：若是$params為字串，並且是Data Source Name，便直接從字串分析出資料庫設定值。
</div>
<pre class="brush: php">
}
</pre>
<div class='alert alert-success'>
第三種載入方式：便是直接傳入$params陣列設定值。上述第一、第二種，其實便是從字串轉為陣列設定值。
</div>
<pre class="brush: php">
// No DB specified yet? Beat them senseless...
if ( ! isset($params['dbdriver']) OR $params['dbdriver'] == '')
{
show_error('You have not selected a database type to connect to.');
}
// Load the DB classes. Note: Since the active record class is optional
// we need to dynamically create a class that extends proper parent class
// based on whether we're using the active record class or not.
// Kudos to Paul for discovering this clever use of eval()
if ($active_record_override !== NULL)
{
$active_record = $active_record_override;
}
require_once(BASEPATH.'database/DB_driver.php');
if ( ! isset($active_record) OR $active_record == TRUE)
{
require_once(BASEPATH.'database/DB_active_rec.php');
if ( ! class_exists('CI_DB'))
{
eval('class CI_DB extends CI_DB_active_record { }');
}
}
else
{
if ( ! class_exists('CI_DB'))
{
eval('class CI_DB extends CI_DB_driver { }');
}
}
</pre>
<div class='alert alert-success'>
第二個參數$active_record_override會決定是否要啟用active record功能。<br/>
CI_DB_active_record類別也是去繼承CI_DB_driver。<br/>
所謂開啟與否就是看CI_DB是否要直接繼承CI_DB_driver。<br/>
參見：<br/>
<a href='db_driver.html'>資料庫基本介面：database/DB_driver.php</a><br/>
<a href='db_active_rec.html'>資料庫擴充介面：database/DB_active_rec.php</a>
</div>
<div class='alert alert-danger'>
為了達到「預設開啟active record」的效果，$active_record_override預設是NULL，接著進行一串判斷。<br/>
何必如此複雜？第二個參數直接寫$active_record = TRUE不就好了。$active_record_override這個變數十分多餘。
</div>
<div class='alert alert-success'>
用eval函數動態定義類別，精彩。相信非必要不應該這樣做。
</div>
<pre class="brush: php">
require_once(BASEPATH.'database/drivers/'.$params['dbdriver'].'/'.$params['dbdriver'].'_driver.php');
// Instantiate the DB adapter
$driver = 'CI_DB_'.$params['dbdriver'].'_driver';
$DB = new $driver($params);
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 */
</pre>
<div class='alert alert-success'>
動態挑選driver類別，接著進行初始化。最後將這個driver實體回傳。
</div>
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