Using inheritance in PHP to add data to array from multiple subclasses

Question

Disclaimer: This is not homework. Also, I'm describing a simplified situation so bear with my semi-psudo code.

I have what I feel is a pretty standard OOP situation, but I'm not sure the best way to handle it. Let's say I have 3 classes: Base, A, and B. Class A extends Base and B extends A. The Base class's constructor performs a database query that pulls various meta data defined in an array. See below:

Class Base {

    public $meta_data = array('col1','col2');

    function __construct() {
        $db->query("select ".join(',',$this->meta_data)." from table");
    }

}

Class A extends Base {

    public $meta_data = array('col3','col4');

    function _construct() {
        parent::__construct();
    }

}

Class B extends A {

    public $meta_data = array('col5','col6');

    function _construct() {
        parent::__construct();
    }

}

When I create a new B() object, I want the Base constructor's sql query to look like this:

select col1, col2, col3, col4, col5, col6 from table;

And when I create a new Base() object, I want the sql query to look like this:

select col1, col2 from table;

Now...I technically know how to accomplish this (in possibly a crude way) but I'm curious what the proper way is without too much code replication and keeping in mind flexibility for the future (ie, adding a subclass of B). I basically need to merge the $meta_data arrays on each inheritance level all the way up to the constructor in the Base class.

Any ideas?

Since each generation of your object has the same attribute, you'd have to do your parent attribue merging in the constructor. PHP does not allow an object attribute to be initialized to anything other than a constant value, so public $meta = array_merge(parent::$meta, ...) is not possible. — Marc B
– Marc B, Commented Feb 3, 2012 at 3:31

Charles Sprayberry · Accepted Answer · 2012-02-03 03:42:02Z

3

When you extend the class and define the new property you are overriding the values set in the parent class. I would wind up removing the $meta_data array from all but Base. Then in your extending classes create a function similar to:

After solving it in a very simple way I wound up deciding I would go with something like the following in Base:

protected function addToMetaData(array $meta_data) {
    $this->meta_data = array_merge($this->meta_data, $meta_data);
}

Then in your extending class constructors you just pass in an array of the values you want to add to Base::$meta_data.

edited Feb 3, 2012 at 3:42

answered Feb 3, 2012 at 3:34

Charles Sprayberry

7,8823 gold badges43 silver badges52 bronze badges

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

1 Comment

Jeff Over a year ago

Thanks for the input...I'm thinking about using something similar to your idea. It's nice and elegant.

Naveen Kumar · Accepted Answer · 2012-02-03 06:09:40Z

0

class base
{
    public $met;

    function __construct()
    {
    $this->met=array("col1","col2");
//      $this->query= "select " . $this->met " from test"; 
    }
}

class a extends base
{

    public $meta;
    function __construct()
    {
        parent::__construct();
            $this->meta =array("col3", "col4" );
        $this->meta=array_merge((array)$this->meta,(array)$this->met);
        print_r($this->meta);
    }

}

class b extends a
{
public $metb;
    function __construct()
    {
        parent::__construct();
            $this->metb =array("col5", "col6" );
        $this->metb=array_merge((array)$this->meta,(array)$this->met);
        print_r($this->metb);
    }
}

answered Feb 3, 2012 at 6:09

Naveen Kumar

4,6011 gold badge20 silver badges39 bronze badges

Comments

Eric · Accepted Answer · 2014-09-16 22:07:04Z

You can build the list in the constructor as well if you use static definitions:

class Base {
    public static $meta_data = array('col1','col2');
    function __construct() {
        $this->meta_data = array();
        $class = $this;
        while ($class) {
            $this->meta_data = array_merge($class::$meta_data, $this->meta_data);
            $class = get_parent_class($class);
        }
        print implode(',', $this->meta_data) . "\n";
    }
}

class A extends Base {
    public static $meta_data = array('col3','col4');
}

class B extends A {
    public static $meta_data = array('col5','col6');
}

new A();
new B();

This will output:

col1,col2,col3,col4
col1,col2,col3,col4,col5,col6

Collectives™ on Stack Overflow

Using inheritance in PHP to add data to array from multiple subclasses

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related