php creating a class variable

Question

Hello i'm using php and i'm trying to make a database class where the constructor will connect the class to the database and assign the pointer to a class variable. The problem that I have is that every time a new instance of the class is created, the constructor gets called and the code connects to the database. I don't see why it should connect to the database every single time that it is called so how would i go about make a class variable that's the same in all the instances and once it is given the pointer, it won't create it again.

Thanks

You might want to read this question and accepted answer: http://stackoverflow.com/questions/9227400/php-singleton-database-connection-is-this-code-bad-practice — summea, Mar 02 '12 at 21:51
I agree with summea, personally I find dependency injection way easier to implement than singleton. — Kisaro, Mar 02 '12 at 21:57

score 2 · Answer 1 · answered Mar 02 '12 at 21:52

Database connection shouldn't go in the constructor. You should have a ConnectionFactory class, which would connect do the database and return a new DatabaseConnection object.

<?php

class ConnectionFactory {
    public static function newConnection($credentials) {
        //Connect to database
        $connection = new PDO(/* Credentials */);
        return $connection;
    }
}

$connection = ConnectionFactory::newConnection(CREDENTIALS);

Thomas Clayson · Answer 2 · 2012-03-02T21:59:25.110

Hi you have two options.

Your best bet is creating a singleton class. This is a class which references itself so that you can never create more than one of it. If you try to create more than one of it it will return the currently initialised version of itself.

Otherwise stick with what you have and just make sure you're not calling new every time.

e.g.

$db = new Database(); // call this once to create
// don't do this again
$anotherdb = new Database();
// just use the db object from before
$db->query("...");

However this might get confusing, and you might lose scope of the variable, so I would suggest going with the singleton method. Some people will tell you not to use singleton's but its up to you. Works well with database classes.

If you look around on the internet you will find examples of other database classes to look at.

Have a look at frameworks like codeigniter too, they use their own database classes. It might be worth looking at how they work.

Singletons are evil. And what if he does need to connect more than once (to a different database, with different credentials)? — Madara's Ghost, Mar 03 '12 at 11:01
I've heard that singletons are evil, but I've never had any problems. And after iOS programming (objective c) I find singletons are very useful. You can create singletons with more than one connection. Create a static variable to hold each connection. In any case, its an answer to help the OP. — Thomas Clayson, Mar 03 '12 at 18:21

score 0 · Answer 3 · answered Mar 05 '12 at 20:44

Instead of making new connection for each class you create, you should create a single connection an share it between the classes.

$connection = new PDO( ... );

$first = new Foo( $connection );
$second = new Bar( $connection );

In this way both instances have access to the same connection.

You also might benefit from watching this video: The Clean Code Talks - Don't Look For Things!

php creating a class variable

3 Answers3