Use singleton pattern to design a PHP database class_PHP tutorial

Recently, I feel that the website’s database is under a lot of pressure, causing the website’s speed to drop significantly. Because a considerable part of the pages are directly connected to the database to read data, this part of the pages is also changed to use the database singleton class to implement. Now the following class is basically used to connect to the database.

<?php
class nmdb 
{
	private $link;
	static private $_instance;
	// 连接数据库
	private function __construct($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;
    }
	
	// 连接数据表
	public function select_db($database)
	{
		$this->result = mysql_select_db($database);
		return $this->result;
	}
	
	// 执行SQL语句
	public function query($query)
	{
		return $this->result = mysql_query($query, $this->link);
	}
	
	// 将结果集保存为数组
	public function fetch_array($fetch_array)
	{
		return $this->result = mysql_fetch_array($fetch_array, MYSQL_ASSOC);
	}
	
	// 获得记录数目
	public function num_rows($query)
	{
		return $this->result = mysql_num_rows($query);
	}
	
	// 关闭数据库连接
	public function close()
	{
		return $this->result = mysql_close($this->link);
	}
	
}
?>

The usage of this class is as follows:

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

You can also refer to the following classes:

<?php
/*
* mysql 单例
*/
class mysql{
    private $host    ='localhost'; //数据库主机
    private $user     = 'root'; //数据库用户名
    private $pwd     = ''; //数据库用户名密码
    private $database = 'imoro_imoro'; //数据库名
    private $charset = 'utf8'; //数据库编码，GBK,UTF8,gb2312
    private $link;             //数据库连接标识;
    private $rows;             //查询获取的多行数组
    static $_instance; //存储对象
    /**
     * 构造函数
     * 私有
     */
    private function __construct($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;
    }
    /**
     * 查询
     */
    public function query($sql, $link = '') {
        $this->result = mysql_query($sql, $this->link) or $this->err($sql);
        return $this->result;
    }
    /**
     * 单行记录
     */
    public function getRow($sql, $type = MYSQL_ASSOC) {
        $result = $this->query($sql);
        return @ mysql_fetch_array($result, $type);
    }
    /**
     * 多行记录
     */
    public function getRows($sql, $type = MYSQL_ASSOC) {
        $result = $this->query($sql);
        while ($row = @ mysql_fetch_array($result, $type)) {
            $this->rows[] = $row;
        }
        return $this->rows;
    }
    /**
     * 错误信息输出
     */
    protected function err($sql = null) {
        //这里输出错误信息
        echo 'error';
        exit();
    }
}
//用例
$db = mysql::getInstance();
$db2 = mysql::getInstance();
$data = $db->getRows('select * from blog');
//print_r($data);
//判断两个对象是否相等
if($db === $db2){
    echo 'true';
}
?>

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