PHP單例模式應(yīng)用示例【多次連接數(shù)據(jù)庫只實(shí)例化一次】

?php
class Singletons{
  // 保存類實(shí)例在此屬性中
  private static $instance;
  // 構(gòu)造方法聲明為private，防止直接創(chuàng)建對象
  private function __construct()
  {
    echo 'Iam constructed';
  }
  // singleton 方法
  public static function singleton()
  {
    if (!isset(self::$instance)) {
      $c = __CLASS__;
      self::$instance =new$c;
    }
    return self::$instance;
  }
  // Example類中的普通方法
  public function bark()
  {
    echo 'Woof!';
  }
  // 阻止用戶復(fù)制對象實(shí)例
  public function __clone()
  {
    trigger_error('Clone is not allowed.',E_USER_ERROR);
  }
}//endclass singletons
  //這個寫法會出錯，因?yàn)闃?gòu)造方法被聲明為private
  //$test= new Singletons();
  // 下面將得到Example類的單例對象
  $test= Singletons::singleton();
  $test->bark();
  // 復(fù)制對象將導(dǎo)致一個E_USER_ERROR.
  $test_clone= clone $test;
?>

private static $_instance;

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

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

?php
 ......
 //初始化一個數(shù)據(jù)庫句柄
 $db = new DB(...);
 //添加用戶信息
 $db->addUserInfo(...);
 ......
//在函數(shù)中訪問數(shù)據(jù)庫，查找用戶信息
function getUserInfo()
{
  $db = new DB(...);//再次new 數(shù)據(jù)庫類，和數(shù)據(jù)庫建立連接
  $db = query(....);//根據(jù)查詢語句訪問數(shù)據(jù)庫
}
?>

?php
 class DB
 {
   private $_db;
   private static $_instance;
   private function __construct(...)
   {
    $this->_db = pg_connect(...);//postgrsql
  }
  private function __clone() {}; //覆蓋__clone()方法，禁止克隆
  public static function getInstance()
  {
    if(! (self::$_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('db.config.php');
     $this->conn = mysql_connect($db['host'],$db['user'],$db['password']);
     if(!mysql_select_db($db['database'],$this->conn)){
      echo "失敗";
    };
    mysql_query('set names utf8',$this->conn);
  }
  public static function getInstance(){
    if(is_null(self::$instance)){
      self::$instance = new db;
    }
    return self::$instance;
  }
  /**
   * 查詢數(shù)據(jù)庫
   */
  public function select($table,$condition=array(),$field = array()){
    $where='';
    if(!empty($condition)){
      foreach($condition as $k=>$v){
        $where.=$k."='".$v."' and ";
      }
      $where='where '.$where .'1=1';
    }
    $fieldstr = '';
    if(!empty($field)){
      foreach($field as $k=>$v){
        $fieldstr.= $v.',';
      }
       $fieldstr = rtrim($fieldstr,',');
    }else{
      $fieldstr = '*';
    }
    self::$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 $resuleRow;
  }
  /**
   * 添加一條記錄
   */
   public function insert($table,$data){
    $values = '';
    $datas = '';
    foreach($data as $k=>$v){
      $values.=$k.',';
      $datas.="'$v'".',';
    }
    $values = rtrim($values,',');
    $datas  = rtrim($datas,',');
    self::$sql = "INSERT INTO {$table} ({$values}) VALUES ({$datas})";
    if(mysql_query(self::$sql)){
      return mysql_insert_id();
    }else{
      return false;
    };
   }
   /**
   * 修改一條記錄
   */
  public function update($table,$data,$condition=array()){
    $where='';
    if(!empty($condition)){
      foreach($condition as $k=>$v){
        $where.=$k."='".$v."' and ";
      }
      $where='where '.$where .'1=1';
    }
    $updatastr = '';
    if(!empty($data)){
      foreach($data as $k=>$v){
        $updatastr.= $k."='".$v."',";
      }
      $updatastr = 'set '.rtrim($updatastr,',');
    }
    self::$sql = "update {$table} {$updatastr} {$where}";
    return mysql_query(self::$sql);
  }
  /**
   * 刪除記錄
   */
   public function delete($table,$condition){
    $where='';
    if(!empty($condition)){
      foreach($condition as $k=>$v){
        $where.=$k."='".$v."' and ";
      }
      $where='where '.$where .'1=1';
    }
    self::$sql = "delete from {$table} {$where}";
    return mysql_query(self::$sql);
   }
  public static function getLastSql(){
    echo self::$sql;
  }
}
$db = db::getInstance();
//$list = $db->select('demo',array('name'=>'tom','password'=>'ds'),array('name','password'));
//echo $db->insert('demo',array('name'=>'最近你啦','password'=>'123'));
//echo $db->update('demo',array("name"=>'xxx',"password"=>'123'),array('id'=>1));
echo $db->delete('demo',array('id'=>'2'));
db::getLastSql();
echo "pre>";
?>