PHP基于单例模式编写PDO类的方法

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：

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());
  }
 }
 
 
 private function __clone() {}
 
 
 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;
 }
 
 
 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;
 }
 
 
 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;
 }
 
 
 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;
 }
 
 
 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;
 }
 
 
 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;
  }
 }
 
 
 public function execSql($strSql, $debug = false)
 {
  if ($debug === true) $this->debug($strSql);
  $result = $this->dbh->exec($strSql);
  $this->getPDOError();
  return $result;
 }
 
 
 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;
 }
 
 
 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'];
 }
 
 
 public function getTableEngine($dbName, $tableName)
 {
  $strSql = "SHOW TABLE STATUS FROM $dbName WHERe Name='".$tableName."'";
  $arrayTableInfo = $this->query($strSql);
  $this->getPDOError();
  return $arrayTableInfo[0]['Engine'];
 }
 
 
 private function beginTransaction()
 {
  $this->dbh->beginTransaction();
 }
 
 
 private function commit()
 {
  $this->dbh->commit();
 }
 
 
 private function rollback()
 {
  $this->dbh->rollback();
 }
 
 
 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;
  }
 }
 
 
 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.");
   }
  }
 }
 
 
 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;
 }
 
 
 private function getPDOError()
 {
  if ($this->dbh->errorCode() != '00000') {
   $arrayError = $this->dbh->errorInfo();
   $this->outputError($arrayError[2]);
  }
 }
 
 
 private function debug($debuginfo)
 {
  var_dump($debuginfo);
  exit();
 }
 
 
 private function outputError($strErrMsg)
 {
  throw new Exception('MySQL Error: '.$strErrMsg);
 }
 
 
 public function destruct()
 {
  $this->dbh = null;
 }
}
?>

四、调用方法：

destruct();
?>

五、总结

以上就是PHP基于单例模式编写PDO类的全部内容，希望对大家学习或者使用PHP能有所帮助，如果有疑问大家可以留言交流，谢谢大家对考高分网的支持。