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);

DBDA类的单例模式和完整功能

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

类的引用