PHP classic interview questions design patterns (frequently encountered), php design patterns_PHP tutorial

PHP classic interview questions design patterns (frequently encountered), PHP design patterns

Design patterns are often mentioned during the interview process, and sometimes we are asked to give examples. Application scenarios of various design patterns.

Using design patterns can reduce our workload and optimize our code.

There are many design patterns. Here we introduce 4 modes: singleton mode, factory mode, combination mode and strategy mode

If there are any problems with the code or a better way, please let me know, thank you!!!!!

/**
 * 单例模式
 * @author YangYang <1812271619@qq.com>
 * 可以想成在一次http请求中只产生该类的一个对象(即只new classname一次)
 * 经典的例子是数据库连接(redis,mongodb,memcache等)
 * 在一次http请求中我们可能需要对数据库做增删改查多条sql操作
 * 但是如果一次http请求中每执行一条sql我们就mysql_connect(),很明显会导致服务器资源的浪费
 * 为了节约资源,就可以通过单例模式来实现一次http请求只做一次mysql_connect()
 * 即将mysql_connect()放在类方法的__construct中,并将__construct方法做成私有,
 * 这样只能通过getInstance()方法来获得mysql_connect()的资源连接符
 * getInstance()方法中判断是否已经存在myql连接符,如果存在就直接返回该连接符
 * 否则new classname()即调用了__construct方法执行了mysql_connect()得到了资源连接符,并返回连接符
 * 因为现在PHP已不再建议直接使用mysql函数进行数据库操作,而是建议通过PDO进行数据库操作,所以这里写一个简易PDO连接的单例模式
 * 这里只是讲解单例原理,数据库的防sql注入等问题不做考虑
 * 准备工作 数据库:test 数据表:user 字段:id name 记录:1 CodeAnti
 * 最终运行结果: 数据表user中id=1这条记录被删除
 */
class SinglePDO
{
    private static $_instance = null;
    private $_pdo;
    //私有,防止外部直接实例化new SinglePDO(...)
    private function __construct($dsn,$dbUser,$dbPassword)
    {
        try{
            $this->_pdo = new PDO($dsn,$dbUser,$dbPassword);
            $this->_pdo->exec('set names utf8');
        }catch(PDOException $e){
            die("Error:{$e->getMessage()}");
        }
    }
    //私有,防止克隆
    private function __clone(){}
    //获取连接实例
    public static function getInstance($dsn,$dbUser,$dbPassword)
    {
        if(self::$_instance === null)
            self::$_instance = new self($dsn,$dbUser,$dbPassword);
        return self::$_instance;
    }
    //执行sql
    public function execSql($sql)
    {
        $result = $this->_pdo->exec($sql);
        return $result;
    }
}

$dsn = "mysql:host=localhost;dbname=test";
$dbUser = "root";
$dbPassword = "";
$sql = "delete from user where id = 1";
$pdo = SinglePDO::getInstance($dsn,$dbUser,$dbPassword);
$result = $pdo->execSql($sql); //$pdo->execSql($sql)多次调用,但仍然是同一个pdo对象
print_r($result);

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