一、单例模式简介简单的说，一个对象（在学习设计模式之前，需要比较了解面向对象思想）只负责一个特定的任务；二、为什么要使用PHP单例模式？1、php的应用主要在于数据库应用, 所以一个应用中会存在大量的数据库操作, 使用单例模式, 则可以避免大量的new 操作消耗的资源。2、如果系统中需要有一个类来全局控制某些配置信息, 那么使用单例模式可以很方便的实现. 这个可以参看ZF的FrontController部分。3、在一次页面请求中, 便于进行调试, 因为所有的代码(例如数据库操作类db)都集中在一个类中, 我们可以在类中设置钩子, 输出日志，从而避免到处var_dump, echo。三、PHP基于单例模式编写PDO类的示例代码代码如下：一、单例模式简介简单的说，一个对象（在学习设计模式之前，需要比较了解面向对象思想）只负责一个特定的任务；二、为什么要使用PHP单例模式？1、php的应用主要在于数据库应用, 所以一个应用中会存在大量的数据库操作, 使用单例模式, 则可以避免大量的new 操作消耗的资源。2、如果系统中需要有一个类来全局控制某些配置信息, 那么使用单例模式可以很方便的实现. 这个可以参看ZF的FrontController部分。3、在一次页面请求中, 便于进行调试, 因为所有的代码(例如数据库操作类db)都集中在一个类中, 我们可以在类中设置钩子, 输出日志，从而避免到处var_dump, echo。三、PHP基于单例模式编写PDO类的示例代码代码如下：
<?php
/*** MyPDO* @author Jason.Wei <jasonwei06@hotmail.com>* @license http://www.sunbloger.com/* @version 5.0 utf8*/
class MyPDO
{protected static $_instance = null;protected $dbName = '';protected $dsn;protected $dbh;/*** 构造* * @return MyPDO*/private function __construct($dbHost, $dbUser, $dbPasswd, $dbName, $dbCharset){try {$this->dsn = 'mysql:host='.$dbHost.';dbname='.$dbName;$this->dbh = new PDO($this->dsn, $dbUser, $dbPasswd);$this->dbh->exec('SET character_set_connection='.$dbCharset.', character_set_results='.$dbCharset.', character_set_client=binary');} catch (PDOException $e) {$this->outputError($e->getMessage());}}/*** 防止克隆* */private function __clone() {}/*** Singleton instance* * @return Object*/public static function getInstance($dbHost, $dbUser, $dbPasswd, $dbName, $dbCharset){if (self::$_instance === null) {self::$_instance = new self($dbHost, $dbUser, $dbPasswd, $dbName, $dbCharset);}return self::$_instance;}/*** Query 查询** @param String $strSql SQL语句* @param String $queryMode 查询方式(All or Row)* @param Boolean $debug* @return Array*/public function query($strSql, $queryMode = 'All', $debug = false){if ($debug === true) $this->debug($strSql);$recordset = $this->dbh->query($strSql);$this->getPDOError();if ($recordset) {$recordset->setFetchMode(PDO::FETCH_ASSOC);if ($queryMode == 'All') {$result = $recordset->fetchAll();} elseif ($queryMode == 'Row') {$result = $recordset->fetch();}} else {$result = null;}return $result;}/*** Update 更新** @param String $table 表名* @param Array $arrayDataValue 字段与值* @param String $where 条件* @param Boolean $debug* @return Int*/public function update($table, $arrayDataValue, $where = '', $debug = false){$this->checkFields($table, $arrayDataValue);if ($where) {$strSql = '';foreach ($arrayDataValue as $key => $value) {$strSql .= ", `$key`='$value'";}$strSql = substr($strSql, 1);$strSql = "UPDATE `$table` SET $strSql WHERE $where";} else {$strSql = "REPLACE INTO `$table` (`".implode('`,`', array_keys($arrayDataValue))."`) VALUES ('".implode("','", $arrayDataValue)."')";}if ($debug === true) $this->debug($strSql);$result = $this->dbh->exec($strSql);$this->getPDOError();return $result;}/*** Insert 插入** @param String $table 表名* @param Array $arrayDataValue 字段与值* @param Boolean $debug* @return Int*/public function insert($table, $arrayDataValue, $debug = false){$this->checkFields($table, $arrayDataValue);$strSql = "INSERT INTO `$table` (`".implode('`,`', array_keys($arrayDataValue))."`) VALUES ('".implode("','", $arrayDataValue)."')";if ($debug === true) $this->debug($strSql);$result = $this->dbh->exec($strSql);$this->getPDOError();return $result;}/*** Replace 覆盖方式插入** @param String $table 表名* @param Array $arrayDataValue 字段与值* @param Boolean $debug* @return Int*/public function replace($table, $arrayDataValue, $debug = false){$this->checkFields($table, $arrayDataValue);$strSql = "REPLACE INTO `$table`(`".implode('`,`', array_keys($arrayDataValue))."`) VALUES ('".implode("','", $arrayDataValue)."')";if ($debug === true) $this->debug($strSql);$result = $this->dbh->exec($strSql);$this->getPDOError();return $result;}/*** Delete 删除** @param String $table 表名* @param String $where 条件* @param Boolean $debug* @return Int*/public function delete($table, $where = '', $debug = false){if ($where == '') {$this->outputError("'WHERE' is Null");} else {$strSql = "DELETE FROM `$table` WHERE $where";if ($debug === true) $this->debug($strSql);$result = $this->dbh->exec($strSql);$this->getPDOError();return $result;}}/*** execSql 执行SQL语句** @param String $strSql* @param Boolean $debug* @return Int*/public function execSql($strSql, $debug = false){if ($debug === true) $this->debug($strSql);$result = $this->dbh->exec($strSql);$this->getPDOError();return $result;}/*** 获取字段最大值* * @param string $table 表名* @param string $field_name 字段名* @param string $where 条件*/public function getMaxValue($table, $field_name, $where = '', $debug = false){$strSql = "SELECT MAX(".$field_name.") AS MAX_VALUE FROM $table";if ($where != '') $strSql .= " WHERE $where";if ($debug === true) $this->debug($strSql);$arrTemp = $this->query($strSql, 'Row');$maxValue = $arrTemp["MAX_VALUE"];if ($maxValue == "" || $maxValue == null) {$maxValue = 0;}return $maxValue;}/*** 获取指定列的数量* * @param string $table* @param string $field_name* @param string $where* @param bool $debug* @return int*/public function getCount($table, $field_name, $where = '', $debug = false){$strSql = "SELECT COUNT($field_name) AS NUM FROM $table";if ($where != '') $strSql .= " WHERE $where";if ($debug === true) $this->debug($strSql);$arrTemp = $this->query($strSql, 'Row');return $arrTemp['NUM'];}/*** 获取表引擎* * @param String $dbName 库名* @param String $tableName 表名* @param Boolean $debug* @return String*/public function getTableEngine($dbName, $tableName){$strSql = "SHOW TABLE STATUS FROM $dbName WHERE Name='".$tableName."'";$arrayTableInfo = $this->query($strSql);$this->getPDOError();return $arrayTableInfo[0]['Engine'];}/*** beginTransaction 事务开始*/private function beginTransaction(){$this->dbh->beginTransaction();}/*** commit 事务提交*/private function commit(){$this->dbh->commit();}/*** rollback 事务回滚*/private function rollback(){$this->dbh->rollback();}/*** transaction 通过事务处理多条SQL语句* 调用前需通过getTableEngine判断表引擎是否支持事务** @param array $arraySql* @return Boolean*/public function execTransaction($arraySql){$retval = 1;$this->beginTransaction();foreach ($arraySql as $strSql) {if ($this->execSql($strSql) == 0) $retval = 0;}if ($retval == 0) {$this->rollback();return false;} else {$this->commit();return true;}}/*** checkFields 检查指定字段是否在指定数据表中存在** @param String $table* @param array $arrayField*/private function checkFields($table, $arrayFields){$fields = $this->getFields($table);foreach ($arrayFields as $key => $value) {if (!in_array($key, $fields)) {$this->outputError("Unknown column `$key` in field list.");}}}/*** getFields 获取指定数据表中的全部字段名** @param String $table 表名* @return array*/private function getFields($table){$fields = array();$recordset = $this->dbh->query("SHOW COLUMNS FROM $table");$this->getPDOError();$recordset->setFetchMode(PDO::FETCH_ASSOC);$result = $recordset->fetchAll();foreach ($result as $rows) {$fields[] = $rows['Field'];}return $fields;}/*** getPDOError 捕获PDO错误信息*/private function getPDOError(){if ($this->dbh->errorCode() != '00000') {$arrayError = $this->dbh->errorInfo();$this->outputError($arrayError[2]);}}/*** debug* * @param mixed $debuginfo*/private function debug($debuginfo){var_dump($debuginfo);exit();}/*** 输出错误信息* * @param String $strErrMsg*/private function outputError($strErrMsg){throw new Exception('MySQL Error: '.$strErrMsg);}/*** destruct 关闭数据库连接*/public function destruct(){$this->dbh = null;}
}
?>
四、调用方法：
<?php
require 'MyPDO.class.php';
$db = MyPDO::getInstance('localhost', 'root', '123456', 'test', 'utf8');//do something...$db->destruct();
?>