CODEWITHSUNDEEP
phpinheritancestatic-members
wmarbut
wmarbut

Reputation: 4705

PHP Class inheritance and static members, the proper way of doing things

I'm writing a lightweight ORM that can map database columns to instance fields with different names

eg.

Database

Object

To do this my original design was something like this

abstract class DbObj {
    /* In a subclass the author would provide the mapping of fileds
     * from the database to the object
     * e.g.
     * array('userid' => 'user_id', 'username' => 'username'....
     */
    protected static $db_to_obj = array();

    /* This would be auto popuplated from $db_to_obj in reverse */
    protected static $obj_to_db = array();

    /* Many Methods truncated... */

    /* Used by magic methods to make sure a field is legit */
    public function isValidField($name) {
         return in_array(strtolower($name), self::$db_to_obj);
    }
}

Then I subclass this out 

class Cat extends DbObj {
     protected static $db_to_obj = array(
         'catsname' => 'name',
         'itsage' => 'age'
     );
}

The isValidField method does not work as expected. Using a debugger or a good ol fashioned var_dump you will find that the value of self::$db_to_obj is that of the parent class. I would understand this if isValidField was static, but it is not. It does have a $this pointer and it does know its class.

Is there a workaround for this behaviour or a better architecture to use?

Upvotes: 0

Views: 100

Answers (2)

Wouter Dorgelo
Wouter Dorgelo

Reputation: 11998

Don't create variables which are protected and static at the same time when using inheritance.

And if you use inheritance, you can/should do something like:

parent::isValidField($name) {
  // code here
}

Upvotes: 1

Parziphal
Parziphal

Reputation: 6922

Here's a solution:

public function isValidField($name) {
  $class = get_class($this);
  return in_array(strtolower($name), $class::$db_to_obj);
}

Upvotes: 1

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