PDO拒绝在多个数据库之间切换！

Question

Please I am very new to PDO, rather a novice at PHP as well. I am currently working on a project that involves connections to many databases: MySQL, MSSQL and Oracle. So I am using the class below, with PDO, for my connection. The class code is below.

class db {

 private static $objInstance; /* * Class Constructor - Create a new database connection if one doesn't exist * Set to private so no-one can create a new instance via ' = new DB();' */ private function __construct() {} /* * Like the constructor, we make __clone private so nobody can clone the instance */ private function __clone() {} /* * Returns DB instance or create initial connection * @param * @return $objInstance; */ public static function getDB($DBtype, $DBindex) { include('vars.inc.php'); if (!self::$objInstance){ $DBid = $DBindex - 1; switch ($DBtype){ case "mysql": self::$objInstance = new PDO("mysql:host=".$dbvars[$DBid][0].";dbname=".$dbvars[$DBid][1], $dbvars[$DBid][2], $dbvars[$DBid][3]); break; case "mssql": self::$objInstance = new PDO("odbc:Driver={SQL Server};Server=".$dbvars[$DBid][0].";Database=".$dbvars[$DBid][1], $dbvars[$DBid][2], $dbvars[$DBid][3]); break; case "oci"; self::$objInstance = new PDO("oci:dbname=//".$dbvars[$DBid][0].":".$dbvars[$DBid][4]."/".$dbvars[$DBid][1], $dbvars[$DBid][2], $dbvars[$DBid][3]); break; // Add other case(s) here if another RDBMS (Relational Database Management system) is used default: break; } self::$objInstance-> setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); } return self::$objInstance; } 

}

And here is the vars include file that is required by the class, I used an array cos I felt this way, new databases can be added easily to the vars file by a non-programmer over time. Of course, here, I have changed the var file values.

define('DB_SERVER', 'localhost');
define('DB_NAME', 'db1name');
define('DB_USER', 'root');
define('DB_PASSWORD', 'rootpass');
define('DB_PORT', '');

define('DB2_SERVER', 'xxx.xxx.xx.xxx');
define('DB2_NAME', 'db2name');
define('DB2_USER', 'root2');
define('DB2_PASSWORD', 'rootpass2');
define('DB2_PORT', '');

define('DB3_SERVER', 'xx.xxx.xxx.xxx');
define('DB3_NAME', db3name');
define('DB3_USER', 'root3');
define('DB3_PASSWORD', 'rootpass3');
define('DB3_PORT', '');

define('DB4_SERVER', 'xxx.xx.xxx.xx');
define('DB4_NAME', 'oracledb');
define('DB4_USER', 'root4');
define('DB4_PASSWORD', 'rootpass4');
define('DB4_PORT', '1521');

$dbvars = array( array(DB_SERVER, DB_NAME , DB_USER, DB_PASSWORD, DB_PORT),
               array(DB2_SERVER, DB2_NAME , DB2_USER, DB2_PASSWORD, DB2_PORT),
               array(DB3_SERVER, DB3_NAME , DB3_USER, DB3_PASSWORD, DB3_PORT),
               array(DB4_SERVER, DB4_NAME , DB4_USER, DB4_PASSWORD, DB4_PORT)               
             );

Now the problem is that, whenever I have connected to one database and try to run my queries on another one, PDO keeps remembering the old database. But if I independently run either query, everything is fine. Can someone please help with this, or suggest a better method? :(

Eg

include('./includes/db.class.php'); try { $result = DB::getDB("mysql", 3)->query("SELECT myrow FROM mytable");

  foreach($result as $row){ print $row['myrow'].'<br />'; } }catch(PDOException $e){ echo $e->getMessage(); } echo "<br />Then<br /><hr /><br />"; try { $result = DB::getDB("mysql", 1)->query("SELECT yourrow FROM yourtable"); foreach($result as $row){ print $row['yourrow'].'<br />' ; } }catch(PDOException $e){ echo $e->getMessage(); } 

In this case, PDO will simply keep checking DATABASE db1name for TABLE yourtable rather than check DATABASE db3name. So PDO will throw an error:

Answer 1

You have it setup as a singleton. So your next call to Db::getDB returns the original instance. If you want to cache the instances for the duration of the script, change $objInstance to an array, and then instead of doing:

if (!self::$objInstance){

Do

$signature = $DBtype . $DBindex;
if (!isset(self::$objInstances[$signature])) {

Of course you'll need to change the assignment lines and the return line as well, but I think you get the idea...

Answer 2

It appears that your getDB function will only connect once because of this line:

if (!self::$objInstance){

So the first time you execute it, it will connect, but on all subsequent calls the logic is ignored.

I suggest adding another property to your class that stores the current DBType and changing your conditional to:

if (!self::$objInstance || $DBtype != self::$dbtype){

You would have to set $dbtype inside each case of the switch statement.