PHP: How Do I Get a MySQL Link Identifier For an Already Open Connection?

Question

When you open a MySQL connection with mysql_connect(), it returns a link identifier. But what if you want to get that link identifier again later in the script? (for example: A plug-in, that needs to open a new database connection, and still access the old one.)

I'm looking for a way to return a link identifier to the last connection opened by mysql_connect(). Is there a function that does this?

Answer 1

No, there isn't. You have to record link identifiers yourself. You could define link identifier as a class property, so that you can easily access it from your methods and don't have to worry about passing it as a variable over and over again.

Answer 2

Use mysql_pconnect, that will do what you want.

First, when connecting, the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection.

You could also use a static or singleton class to handle connection pooling for you.

<?php
class dbConnectionPooler
{
    static var $connections = array();

    private static function createConnection($host, $username, $password, $db) {
        $connection = mysql_pconnect($host, $username, $password);

        if (FALSE !== $connection) {
            $result = mysql_select_db($db, $connection);

            if (FALSE !== $result) {
                self::$connections[self::getConnectionHash($host, $username, $password, $db)] = $connection;

                return $connection;
            }
        }
    }    

    private static function getConnectionHash($host, $username, $password, $db) {
        return md5($host. $username. $password. $db); // use your favourite hashing function here
    }

    public static function getConnection($host, $username, $password, $db) {
        $connectionHash = self::getConnectionHash($host, $username, $password, $db);

        if (array_key_exists($connectionHash, self::$connections)) {
            return self::$connections[$connectionHash];
        } else {
            return self::createConnection($host, $username, $password, $db);
        }

        return false;
    }
}

$connection = dbConnectionPooler::getConnection("dbhost", "dbuser", "dbpassword", "mydb");
?>

Answer 3

You have to store your handle in a var.

$link = mysql_connect($host, $login, $pass);

And you can reuse $link along your script, before a new HTTP request.

Answer 4

You either have to store the link identifier yourself as mentioned in other answers OR you can simply omit it, the mysql_* functions can reuse the existing handle

mysql_query help explains it like this:

resource mysql_query  ( string $query  [, resource $link_identifier  ] )

link_identifier

    The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed.

I would not use that reuse behaviour myself though, unless you are completely sure that your application (or any plugins, etc) are not opening any new connections to other databases.

Answer 5

Thanks to everyone for the replies.

I ended up opening my own connection, and when my plug-in was done, the last line reopens the initial connection so the rest of the main script can use the database it expects. It's sloppy, I know, but it doesn't seem like there's a better option in this case. :/

Update:: I've submitted this as a feature request on php.net. The link is: http://bugs.php.net/bug.php?id=49400