用單例模式來設計一個PHP數據庫類

最近感覺網站的數據庫壓力比較大，造成網站的速度下降得很厲害。因為有相當一部分的頁面是直接連接數據庫讀數據的，所以把這部分的頁面也改為使用數據庫單例類來實現。現在基本都統一使用下面這個類來連接數據庫了。

<?php
class nmdb 
{
	private $link;
	static private $_instance;
	// 連接數據庫
	private function __construct($host, $username, $password)
	{
		$this->link = mysql_connect($host, $username, $password);
		$this->query("SET NAMES 'utf8'", $this->link);
		//echo mysql_errno($this->link) . ": " . mysql_error($link). "n";
		//var_dump($this->link);
		return $this->link;
	}
	
	private function __clone(){}
	
	public static function get_class_nmdb($host, $username, $password)
	{
        //$connector = new nmdb($host, $username, $password);
        //return $connector;
		
		if( FALSE == (self::$_instance instanceof self) )
		{
			self::$_instance = new self($host, $username, $password);
		}
		return self::$_instance;
    }
	
	// 連接數據表
	public function select_db($database)
	{
		$this->result = mysql_select_db($database);
		return $this->result;
	}
	
	// 執行SQL語句
	public function query($query)
	{
		return $this->result = mysql_query($query, $this->link);
	}
	
	// 將結果集保存為數組
	public function fetch_array($fetch_array)
	{
		return $this->result = mysql_fetch_array($fetch_array, MYSQL_ASSOC);
	}
	
	// 獲得記錄數目
	public function num_rows($query)
	{
		return $this->result = mysql_num_rows($query);
	}
	
	// 關閉數據庫連接
	public function close()
	{
		return $this->result = mysql_close($this->link);
	}
	
}
?>

這個類的使用如下：

$connector = nmdb::get_class_nmdb($host, $username, $password);
$connector -> select_db($database);

下面的類也可以參考下：

<?php
/*
* mysql 單例
*/
class mysql{
    private $host    ='localhost'; //數據庫主機
    private $user     = 'root'; //數據庫用戶名
    private $pwd     = ''; //數據庫用戶名密碼
    private $database = 'imoro_imoro'; //數據庫名
    private $charset = 'utf8'; //數據庫編碼，GBK,UTF8,gb2312
    private $link;             //數據庫連接標識;
    private $rows;             //查詢獲取的多行數組
    static $_instance; //存儲對象
    /**
     * 構造函數
     * 私有
     */
    private function __construct($pconnect = false) {
        if (!$pconnect) {
            $this->link = @ mysql_connect($this->host, $this->user, $this->pwd) or $this->err();
        } else {
            $this->link = @ mysql_pconnect($this->host, $this->user, $this->pwd) or $this->err();
        }
        mysql_select_db($this->database) or $this->err();
        $this->query("SET NAMES '{$this->charset}'", $this->link);
        return $this->link;
    }
    /**
     * 防止被克隆
     *
     */
    private function __clone(){}
    public static function getInstance($pconnect = false){
        if(FALSE == (self::$_instance instanceof self)){
            self::$_instance = new self($pconnect);
        }
        return self::$_instance;
    }
    /**
     * 查詢
     */
    public function query($sql, $link = '') {
        $this->result = mysql_query($sql, $this->link) or $this->err($sql);
        return $this->result;
    }
    /**
     * 單行記錄
     */
    public function getRow($sql, $type = MYSQL_ASSOC) {
        $result = $this->query($sql);
        return @ mysql_fetch_array($result, $type);
    }
    /**
     * 多行記錄
     */
    public function getRows($sql, $type = MYSQL_ASSOC) {
        $result = $this->query($sql);
        while ($row = @ mysql_fetch_array($result, $type)) {
            $this->rows[] = $row;
        }
        return $this->rows;
    }
    /**
     * 錯誤信息輸出
     */
    protected function err($sql = null) {
        //這裡輸出錯誤信息
        echo 'error';
        exit();
    }
}
//用例
$db = mysql::getInstance();
$db2 = mysql::getInstance();
$data = $db->getRows('select * from blog');
//print_r($data);
//判斷兩個對象是否相等
if($db === $db2){
    echo 'true';
}
?>