Inheriting database connection in PHP OOP

Question

My abstract class Database is made for database interaction and any child of this class (UserDatabase, ActionDatabase, EventDatabase) inherits its database connection which is defined as static.

abstract class Database {  
    public static $connection;   
    public function __construct( ) {      
        ...  
        $this->connection = mysql_connect( $host, $username, $password );      
    }  
}     
class UserDatabase extends Database {  
    public function verify( ) {
        if ( $this->connection == parent::$connection ) {
            print "true";  
        } else {  
            print "false";  
            print "this:" . $this->connection . " parent:" . parent::$connection;  
        }  
    }    
}  
$instance = new UserDatabase( );  
$instance->verify( );  
// this prints false, as parent::$connection is empty

Does that mean, that my database connection is only set up and stored in memory once and passed on to subclasses as reference without being replicated for each instance?

Is this how you would implement you OOP-correct database interface?

Scott Saunders · Accepted Answer · 2010-05-13 14:38:35Z

3

Ignoring your code for a moment and looking only at your description of how this scheme should work... Yes, the database connection would only be set up once for each PHP script and would not be duplicated for each instance.

Whether this is a good idea or not depends on what your subclasses are. Each class should have one responsibility. As long as the subclasses' only responsibility is DB interaction, you're probably fine. (Look at the Repository Pattern for an explanation of how this is commonly done.) If your User class extends Database so that it can store itself, you've crossed a line and are writing classes that will have too many dependencies and responsibilities.

As for your code... Almost every line of your code is wrong. You cannot initialize class variables to the results of a function. Your SQL is wrong. The line $connection ? "connected" : "not connected"; does nothing. Almost none of that should be done in a constructor. Etc.

answered May 13, 2010 at 14:38

Scott Saunders

30.5k14 gold badges60 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

sdkfasldf Over a year ago

You're absolutely right, I was trying to illustrate the purpose of the class as short as possible, but I guess my PHP-grammar failed me. My User instance is something UserDatabase returns. User class is just a setter/getter class for values that system may need while it processes the script. When script is finalized it passes User object to current UserDatabase, so it can strip down User to values and then send the update query to database-server. So class Database inheritance chain is separated from the type it returns. ActionDatabase returns and accepts an instance of Action.

jlindenbaum · Accepted Answer · 2010-05-13 14:44:31Z

1

That pattern is OK if you're doing nothing else with those classes but database interactions.

Otherwise you may be better off with a Database class that's created once that you can "getInstance()" of each time. Singleton Design Pattern.

http://www.tonymarston.net/php-mysql/singleton.html

answered May 13, 2010 at 14:44

jlindenbaum

1,88118 silver badges28 bronze badges

Collectives™ on Stack Overflow

Inheriting database connection in PHP OOP

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related