设计模式-单例模式(php)

<?php

//单例模式的实现
class MysqlInstance
{
    private static $instance;//不可被类外部访问
    private $client;
    private $param = array();

    private function __construct()
    {


    }

    //实例化对象
    public static function getInstance()
    {

        if (empty(self::$instance)) {
            self::$instance = new MysqlInstance();
        }
        return self::$instance;
    }

    //设置连接参数
    public function setClientParam($key, $value)
    {
        $this->param[$key] = $value;
    }

    //设置连接对象
    public function setClient()
    {
        try {
            $this->client = new PDO("mysql:host=" . $this->param["server"] . ";dbname=" . $this->param["dbname"], $this->param["username"], $this->param["pwd"]);
            $this->client->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        } catch (\PDOException $exception) {
            echo $exception->getMessage();
        }
    }

    //查询select
    public function getQuery($sql)
    {
        $re=$this->client->prepare($sql);
        $re->execute();
        return $re->fetchAll();
    }

    //事物查询
    public function tranQuery($sql){
        $t=$this->client->prepare($sql);
       return $t->execute();
    }

}


//初始化
$obj = MysqlInstance::getInstance();
$obj->setClientParam("server", "127.0.0.1");
$obj->setClientParam("dbname", "test");
$obj->setClientParam("username", "root");
$obj->setClientParam("pwd", "root123");
$obj->setClient();
$re = $obj->getQuery("select * from user");
unset($obj);//删除对象后重新实例化之后对象参数依然存在
$obj2 = MysqlInstance::getInstance();
//$t=$obj2->tranQuery("insert into user (username,state) VALUES ('index',1)");
$re = $obj2->getQuery("select * from user");
var_dump($re);

在一个对象中，类的属性变量只需要设置一次，不需要进行重复的设置，如上述实现的mysql的连接的类，我们只需要进行一次连接参数设置，当引用之后的类被注销之后，再次实例化设置的参数依然存在，单例模式是对全局变量的一种改进。欢迎扫码关注微信公众号奋斗的猿类，有不足之处欢迎指正。

设计模式-单例模式(php)

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