Magento getSingleton() vs getModel() issue

Question

I want to loop over an array of product IDs in Magento. In the loop I am displaying some custom attributes of the products as:

foreach ($products as $product) {
   $model = Mage::getSingleton('catalog/product')->load($product['id']);
   echo '<br>' . $model->getCredits();
}

Problem is that if the value of getCredits() for the first item is true then all the subsequent items show true even if they do not have the value true.

But when I use Mage::getModel() instead of Mage::getSingleton(), the attribute values are displayed correct.

Can anyone please explain this difference?

Answer 1

Mage::getModel() will always return a new Object for the given model:

/**
 * Retrieve model object
 *
 * @link    Mage_Core_Model_Config::getModelInstance
 * @param   string $modelClass
 * @param   array|object $arguments
 * @return  Mage_Core_Model_Abstract|false
 */
public static function getModel($modelClass = '', $arguments = array())
{
    return self::getConfig()->getModelInstance($modelClass, $arguments);
}

Mage::getSingleton() will check whether the Object of the given model already exists and return that if it does. If it doesn't exist, it will create a new object of the given model and put in registry that it already exists. Next call will not return a new object but the existing one:

/**
 * Retrieve model object singleton
 *
 * @param   string $modelClass
 * @param   array $arguments
 * @return  Mage_Core_Model_Abstract
 */
public static function getSingleton($modelClass='', array $arguments=array())
{
    $registryKey = '_singleton/'.$modelClass;
    if (!self::registry($registryKey)) {
        self::register($registryKey, self::getModel($modelClass, $arguments));
    }
    return self::registry($registryKey);
}

In your case you always want a completely new Product object/model since every product is unique...