database parameters on function __construct

kingdm

I am wondering if my understanding is right.

I placed my database connection parameter on my __construct(), so this means every time the class is instantiated, I also reconnect to my database, right?

private $handle;
public function __construct()
{
  $username = "test";
  $password = "**********";
  $host = "localhost";
  $db = "miner";
  $dsn = 'mysql:dbname='.$db.';host='.$host;
  try {
    $this->handle = new PDO($dsn,$username,$password);
  }
  catch(PDOException $e) {
    print $e->getMessage();
    die();
  }
}

Is this a good practice if I have many request from a certain user? Does this mean every time a user make a request (even if the request is just done minutes ago) the script should first connect to the database? Is there any appropriate way I can preserve my $handle?

BTW: The database connection is working fine.

traq

You'll only have a single connection if you only instantiate the class once.

BTW: you should not post sensitive information - usernames/passwords, for example - online. I'd highly recommend obfuscating them.

Weedpacket

Each request that runs will involve making a new connection, which will be closed when the response is completed (if you don't explicitly close the connection first). This is the usual behaviour (and in line with the principle of HTTP being a stateless protocol).

See [man]pdo.connections[/man] for information about connection handling, including the use of persistent connections.

sneakyimp

kingdm;11017043 wrote:
I placed my database connection parameter on my __construct(), so this means every time the class is instantiated, I also reconnect to my database, right?

By 'request', I think Weedpacket means each user request to your script. Strictly speaking, I wonder if that is true or whether one separate connection will be made for each instance of your class that you instantiate. According to the documentation Weedpacket linked,

PHP Documentation wrote:
Connections are established by creating instances of the PDO base class...Upon successful connection to the database, an instance of the PDO class is returned to your script. The connection remains active for the lifetime of that PDO object. To close the connection, you need to destroy the object by ensuring that all remaining references to it are deleted--you do this by assigning NULL to the variable that holds the object. If you don't do this explicitly, PHP will automatically close the connection when your script ends.

I believe that if you created two separate instances of your class, then you would get two distinct connections to the db, but am not sure about that. Perhaps PDO is smart enough to re-use a connection?

kingdm;11017043 wrote:
Is this a good practice if I have many request from a certain user? Does this mean every time a user make a request (even if the request is just done minutes ago) the script should first connect to the database? Is there any appropriate way I can preserve my $handle?

According to that same link Weedpacket offered:

PHP Documentation wrote:
Many web applications will benefit from making persistent connections to database servers. Persistent connections are not closed at the end of the script, but are cached and re-used when another script requests a connection using the same credentials. The persistent connection cache allows you to avoid the overhead of establishing a new connection every time a script needs to talk to a database, resulting in a faster web application.

You can dictate whether your script uses persistent connections or not by setting certain parameters. I've had problems with scripts configured to use them wherein the server runs out of connections -- I.e., the server exceeds the maximum number of permissible connections. On the other hand, I had a code review once where I was chastised for not using them. Apparently they can result in greater efficiency in high-load situations. This page looks pretty informative. A google search yields lots of discussion on this topic.

Weedpacket

sneakyimp wrote:
I wonder if that is true or whether one separate connection will be made for each instance of your class that you instantiate.

Yes, but traq already covered that, and kingdm is asking about "every time a user make a request (even if the request is just done minutes ago)".