PHP 싱글톤 패턴 분석과 실전을 해결하는 한 가지 비법

private static $_instance;

private function __construct() 
{ 
    $this->_db = pg_connect('xxxx');
} 
private function __clone()
{
}//覆盖__clone()方法，禁止克隆

    public static function getInstance()  
    {  
        if(! (self::$_instance instanceof self) ) 
        {  
            self::$_instance = new self();  
        }
        return self::$_instance;  

    }

<?php
......
//初始化一个数据库句柄
$db = new DB(...);

//添加用户信息
$db->addUserInfo(...);

......

//在函数中访问数据库，查找用户信息
function getUserInfo()
{
    $db = new DB(...);//再次new 数据库类，和数据库建立连接
    $db = query(....);//根据查询语句访问数据库
}

?>

<?php

class DB  
{  
    private $_db;  
    private static $_instance;  
  
    private function __construct(...)  
    {  
        $this->_db = pg_connect(...);//postgrsql  
    }  
  
    private function __clone() {};  //覆盖__clone()方法，禁止克隆  
  
    public static function getInstance()  
    {  
        if(! (self::$_instance instanceof self) ) {  
            self::$_instance = new self();  
        }  
        return self::$_instance;  
    }  
  
    

    public function addUserInfo(...)
    {

   

    }

     public function getUserInfo(...)
    { 

    }

}

//test

$db = DB::getInstance();

$db->addUserInfo(...);

$db->getUserInfo(...);


?>

<?php
class db {
	public $conn;
	public static $sql;
	public static $instance=null;
	private function __construct(){
		require_once(&#39;db.config.php&#39;);
		$this->conn = mysql_connect($db[&#39;host&#39;],$db[&#39;user&#39;],$db[&#39;password&#39;]);
		if(!mysql_select_db($db[&#39;database&#39;],$this->conn)){
			echo "失败";
		};
		mysql_query(&#39;set names utf8&#39;,$this->conn);		
	}
	public static function getInstance(){
		if(is_null(self::$instance)){
			self::$instance = new db;
		}
		return self::$instance;
	}
	/**
	 * 查询数据库
	 */
	public function select($table,$condition=array(),$field = array()){
		$where=&#39;&#39;;
		if(!empty($condition)){
			
			foreach($condition as $k=>$v){
				$where.=$k."=&#39;".$v."&#39; and ";
			}
			$where=&#39;where &#39;.$where .&#39;1=1&#39;;
		}
		$fieldstr = &#39;&#39;;
		if(!empty($field)){
			
			foreach($field as $k=>$v){
				$fieldstr.= $v.&#39;,&#39;;
			}
			 $fieldstr = rtrim($fieldstr,&#39;,&#39;);
		}else{
			$fieldstr = &#39;*&#39;;
		}
		self::$sql = "select {$fieldstr} from {$table} {$where}";
		$result=mysql_query(self::$sql,$this->conn);
		$resuleRow = array();
		$i = 0;
		while($row=mysql_fetch_assoc($result)){
			foreach($row as $k=>$v){
				$resuleRow[$i][$k] = $v;
			}
			$i++;
		}
		return $resuleRow;
	}
	/**
	 * 添加一条记录
	 */
	 public function insert($table,$data){
	 	$values = &#39;&#39;;
	 	$datas = &#39;&#39;;
	 	foreach($data as $k=>$v){
	 		$values.=$k.&#39;,&#39;;
	 		$datas.="&#39;$v&#39;".&#39;,&#39;;
	 	}
	 	$values = rtrim($values,&#39;,&#39;);
	 	$datas   = rtrim($datas,&#39;,&#39;);
	 	self::$sql = "INSERT INTO  {$table} ({$values}) VALUES ({$datas})";
		if(mysql_query(self::$sql)){
			return mysql_insert_id();
		}else{
			return false;
		};
	 }
	 /**
	  * 修改一条记录
	  */
	public function update($table,$data,$condition=array()){
		$where=&#39;&#39;;
		if(!empty($condition)){
			
			foreach($condition as $k=>$v){
				$where.=$k."=&#39;".$v."&#39; and ";
			}
			$where=&#39;where &#39;.$where .&#39;1=1&#39;;
		}
		$updatastr = &#39;&#39;;
		if(!empty($data)){
			foreach($data as $k=>$v){
				$updatastr.= $k."=&#39;".$v."&#39;,";
			}
			$updatastr = &#39;set &#39;.rtrim($updatastr,&#39;,&#39;);
		}
		self::$sql = "update {$table} {$updatastr} {$where}";
		return mysql_query(self::$sql);
	}
	/**
	 * 删除记录
	 */
	 public function delete($table,$condition){
	 	$where=&#39;&#39;;
		if(!empty($condition)){
			
			foreach($condition as $k=>$v){
				$where.=$k."=&#39;".$v."&#39; and ";
			}
			$where=&#39;where &#39;.$where .&#39;1=1&#39;;
		}
		self::$sql = "delete from {$table} {$where}";
		return mysql_query(self::$sql);
		
	 }
	
	public static function getLastSql(){
		echo self::$sql;
	}
	
	
	
}

$db = db::getInstance();
//$list = $db->select(&#39;demo&#39;,array(&#39;name&#39;=>&#39;tom&#39;,&#39;password&#39;=>&#39;ds&#39;),array(&#39;name&#39;,&#39;password&#39;));
//echo $db->insert(&#39;demo&#39;,array(&#39;name&#39;=>&#39;最近你啦&#39;,&#39;password&#39;=>&#39;123&#39;));
//echo $db->update(&#39;demo&#39;,array("name"=>&#39;xxx&#39;,"password"=>&#39;123&#39;),array(&#39;id&#39;=>1));
echo $db->delete(&#39;demo&#39;,array(&#39;id&#39;=>&#39;2&#39;));
db::getLastSql();
echo "<pre class="brush:php;toolbar:false">";
?>