PDO Wrapper

<?php

/**
 * PHP PDO Wrapper for multiple databases.
 *
 * PHP version 5.5+
 *
 * LICENSE: 
 * Feel free to use this code however you please.
 * I only ask to leave this comment as it is.
 * Also, I'd appreciate a message if you use it
 * and or have suggestions to improve it.
 *
 * @category   Database Class
 * @author     Johan Kruse <johan dot kruse at gmail>
 * @version    0.1
 */
 
  class DatabaseException extends Exception{}
  
  abstract class Database extends PDO{
    public $sth;
    
    abstract protected function sqlTableExists();
    abstract protected function sqlSelectDatabase();
    
    private function getDSN($driver, $multiarg){
      return "$driver:" . implode(';', array_map(function($v, $k){return "$k=$v";}, $multiarg, array_keys($multiarg)));
    }
    
    private function getParamType($type){
      switch($type){
        case 'string':   return parent::PARAM_STR;
        case 'integer':  return parent::PARAM_INT;
        case 'boolean':  return parent::PARAM_BOOL;
        case 'NULL':     return parent::PARAM_NULL;
        case 'double':   return parent::PARAM_STR;
        case 'resource': return parent::PARAM_LOB;
        default: 
          throw new DatabaseException("Unsupported variable type: '$type' parsed in query.");
      }
    }
    
    public function prepare($sql, $options = array()){
      $this->sth = parent::prepare($sql, $options);
      return $this;
    }
    public function query($stmt){
      return $this->sth = parent::query($stmt);  
    }
       
    public function execute(){
      for($i = 0; $i < func_num_args(); $i++){
        if(($type = gettype(($var = func_get_arg($i)))) == 'array'){
          foreach($var as $key => $val){
            if($type = (gettype($key) == 'string')){
              $this->sth->bindValue(($key[0] != ':') ? ":$key" : $key, $val, $this->getParamType($type));
            } else {
              throw new DatabaseException("Unsupported array index, expected named parameter.");
            }            
          }
        } else {
          $this->sth->bindValue($i+1, $var, $this->getParamType($type));
        }
      }
      
      $this->sth->execute();
      return $this->sth;
    }

    public function fetchAssoc(){
      return $this->sth->fetch(PDO::FETCH_ASSOC);
    }
    public function fetchBoth(){
      return $this->sth->fetch(PDO::FETCH_BOTH);
    }
    public function fetchNum(){
      return $this->sth->fetch(PDO::FETCH_NUM);
    }
    public function fetchObj(){
      return $this->sth->fetch(PDO::FETCH_OBJ);
    }
    public function fetchLazy(){
      return $this->sth->fetch(PDO::FETCH_LAZY);
    }
       
    public function tableExists($name){
      return $this->prepare($this->sqlTableExists())->execute($name)->rowCount() > 0;
    }
    
    public function selectDatabase($name){
      return $this->prepare($this->sqlSelectDatabase())->execute($name);
    }
           
    function __construct($username, $password, $dsn, $options){
      if(in_array($driver = strtolower(get_class($this)), parent::getAvailableDrivers())){
        $dsn = gettype($dsn) == 'array' ? $this->getDSN($driver, $dsn) : (string) $dsn;
        
        if(gettype($options) == 'array'){
          $options[parent::ATTR_EMULATE_PREPARES] = true;
          $options[parent::ATTR_ERRMODE] = parent::ERRMODE_EXCEPTION;
          
          try{
            parent::__construct($dsn, $username, $password, $options);
          } catch(PDOException $e){
            throw new DatabaseException('Could not connect to the database server.', $e);
          }          
        } else {
          throw new DatabaseException('Expected an array of options.', $e);
        }
      } else {
        throw new DatabaseException("Database driver '$driver' is not supported on this machine.'");
      }
    }
  }
  
  class MySQL extends Database{   
    protected function sqlTableExists(){
      return 'SHOW TABLES LIKE ?';
    }
    protected function sqlSelectDatabase(){
      return "USE ?";
    }
    
    function __construct($username, $password, $dsn, $options = array()) {
      parent::__construct($username, $password, $dsn, $options);
    }
  }
  
  class PostgreSQL extends Database{
    function sqlTableExists(){
      return "SELECT count(*) FROM pg_class WHERE relname=? AND relkind='r'";
    }
    function sqlSelectDatabase(){
      throw new DatabaseException('PostgrSQL does not support database swapping, create a new link or select from "db.table".');
    }       
    
    function __construct($username, $password, $dsn, $options = array()) {
      parent::__construct($username, $password, $dsn, $options);
    }
  }
  
?>