Question

If I want to get a customer’s email address from a database, the following is bad, because $row will contain an element for every single field in the customer table:

$result = mysqli_query ('SELECT * FROM customer WHERE custid = 1');
$row = mysqli_fetch_array ($result, MYSQLI_ASSOC);

This is considered better, because $row will contain a single element for the email address, which is all we need:

$result = mysqli_query ('SELECT email FROM customer WHERE custid = 1');
$row = mysqli_fetch_array ($result, MYSQLI_ASSOC);

I am trying to apply the same logic to objects. If a “customer” object has say 50 properties/fields, is it common to populate all 50 properties when you only need to access one?

Below is a basic example of a customer class and object which is resource hungry if all we want to do is get a customer’s email address, and not all their other details (in this example a “customer” object has 5 properties but in reality there could be many more):

class Customer {

    private $custid;
    private $firstname;
    private $lastname;
    private $email;
    private $dateadded;

    public function getCustomer ($id) {
        $result = mysql_queryi ('SELECT * FROM customer WHERE custid = ' . $id);
        $row = mysqli_fetch_array ($result, MYSQLI_ASSOC);
        foreach ($row as $key => $value) {
            if (isset ($this->$key)) {
                $this->$key = $value;
            }
        }
    }
}

$customer = new Customer ();
$customer->getCustomer (1); // All I wanted is the email address, but now I have everything :-(

Answer 1

You could make a second argument to your getCustomer function that accepts an array of fields to query

public function getCustomer ($id, $fields=array('*')) {
    $fields = implode(',', $fields);
    $result = mysql_queryi("SELECT {$fields} FROM customer WHERE ...");
    // ...

Usage

// get entire customer
$customer->getCustomer(1);

// just get the email field
$customer->getCustomer(1, array('email'));

// get full name
$customer->getCustomer(1, array('firstname', 'lastname'));

---

Bonus:

I’d recommend storing your fields a little differently in your model

class Customer
    private $_data;

    public function getCustomer($id, $fields=array('*')) {
        // ...
    }

    // PHP magic set method
    // calling $this->foo = 'bar' results in $this->_data['foo'] = 'bar'
    public function __set($key, $value) {
        return $this->_data[$key] = $value;
    }

    // PHP magic get method
    // calling $this->foo results in $this->_data['foo']
    public function __get($key) {
        return array_key_exists($key, $this->_data)
            ? $this->_data[$key]
            : null
        ;
    }
}

This way you can get rid of all the statically defined instance variables; e.g., private $custid;, private $firstname;, private ...

Instead, all fields will be stored in $this->_data private associative array.

What’s sweet about this is you don’t even have to change the way your getCustomer function is written.

Learn more about PHP magic methods