0606-工厂模式、单例模式、DBDA的单例和完整功能

工厂模式：只要指定类名，就可以据此获取一个该类的对象。

单例模式：某个类，只允许其“创建”出一个对象。

单例的方法：三私一公（一个私有化对象，一个私有化构造方法，一个私有化克隆方法，一个公共方法返回对象）。

DBDA类的单例模式和完整功能：

<?php
//$db = new mysqli('localhost:3306','root','','per_position');
echo '<meta charset="utf-8">';
class DBDA{
    //定义数据库链接参数
    public $host = 'localhost';
    public $user = 'root';
    public $pwd = '';
    public $database = 'per_position';
    public $charset = 'utf8';
    
    //数据库连接对象
    public $db = null;
    //DBDA对象
    private static $link = null;
    
    //禁止构造：初始化数据
    private function __construct($configArr=array()){
        $this->host = isset($configArr['host']) ? $configArr['host'] : 'localhost';
        $this->user = isset($configArr['user']) ? $configArr['user'] : 'root';
        $this->pwd = isset($configArr['pwd']) ? $configArr['pwd'] : '';
        $this->database = isset($configArr['database']) ? $configArr['database'] : 'per_position';
        $this->charset = isset($configArr['charset']) ? $configArr['charset'] : 'utf8';
        //链接数据库
        $this->connect();
    }
    //禁止克隆
    private function __clone(){}
    //提供公有方法返回对象
    static function getDb($config=array()){
        if(!isset(self::$link)){
            self::$link = new self($config);
        }
        return self::$link;
    }
    //链接数据库的方法
    function connect(){
        $this->db = new mysqli($this->host,$this->user,$this->pwd,$this->database);
        !mysqli_connect_error() or die('连接失败');
        $this->db->query('set names '.$this->charset);
    }
    //执行sql语句的方法
    function query($sql){
        $res = $this->db->query($sql);
        if(!$res){
            echo ("<br />执行失败。");
            echo "<br />失败的sql语句为：" . $sql;
            echo "<br />出错信息为：" . mysqli_error($this->db);
            echo "<br />错误代号为：" . mysqli_errno($this->db);
            die();
        }
        return $res;
    }
    //返回二维数组
    function getAll($sql){
        $res = $this->query($sql);
        return $res->fetch_all();
    }
    //返回字符串
    function getStr($sql){
        $res = $this->query($sql);
        $arr = $res->fetch_all();
        $str = '';
        foreach($arr as $v){
            foreach($v as $vv){
                $str .= $vv.",";
            }
            $str = substr($str,0,-1);
            $str .= "^";
        }
        $str =  substr($str,0,-1);
        return $str;
    }
    //返回json
    function getJson($sql){
        $res = $this->query($sql);
        $arr = $res->fetch_all();
        return json_encode($arr);
    }
    //返回关联数组
    function getAssoc($sql){
        $res = $this->query($sql);
        $arr = array();
        while($row = $res->fetch_assoc()){
            $arr[$row['department']]=$row;
        }
        return $arr;
    }
}
//$config = array(
//    //'database' => 'mysql'
//);
//$DBDA = new DBDA();
//var_dump($DBDA->getJson('select * from user'));
//看错误提示
//$DBDA->query('select * from 123');
//$res = $DBDA->db->query('select * from user');
//var_dump($res->fetch_all());



//禁用了构造方法，直接new会报错。
//$DBDA = DBDA::getDb();
//var_dump($DBDA);
//echo "<br>";
//$DBDA = DBDA::getDb();
//var_dump($DBDA);

<?php
include('DBDA.class.php');
$dbda = DBDA::getDb();
var_dump($dbda->getAll('select * from user'));