understanding self::DISPLAY_TYPE_NEW_PRODUCTS

Question

I am learning magento and I have some doubts about how it works, could someone help me with it or can suggest some tutorial from where I can learn more about magento. In

/app/design/frontend/../../template/catalog/product/widget/new/content/new_grid.phtml

file there is a piece of code

$this->getProductCollection()

I know this function can be found in

/app/code/core/Mage/Catalog/Block/Product/Widget/New.php

But there is no such function, I also looked in the parent class and there also I could not find this function.

I found another function in

/app/code/core/Mage/Catalog/Block/Product/Widget/New.php

Below is the function

protected function _getProductCollection()
{
    switch ($this->getDisplayType()) {
        case self::DISPLAY_TYPE_NEW_PRODUCTS:
            $collection = parent::_getProductCollection();
            break;
        default:
            $collection = $this->_getRecentlyAddedProductsCollection();
            break;
    }
    return $collection;
}

and I know this function is called but my question is why and how? These two have different names then how they can be same. Do it means that "_" is only used if a function is protected and it does not have to do anything with the function name.

And also when I echoed

$this->getDisplayType()

then I got 'new_products' but if you see in this function then magento is using self::DISPLAY_TYPE_NEW_PRODUCTS in case then how these two cases or strings are similar.

Also please explain this line

parent::_getProductCollection()

do it means call _getProductCollection() from parent class and if yes then where this is specified in magento.

Answer 1

1) Regarding: $this->getProductCollection() method:

Check file:

/app/code/core/Mage/Catalog/Block/Product/Widget/New.php

This is having _beforeToHtml() method at line no.127(Line number can be different for different version of Magento).

/**
 * Prepare collection with new products
 *
 * @return Mage_Core_Block_Abstract
 */
protected function _beforeToHtml()
{
    $this->setProductCollection($this->_getProductCollection());
    return parent::_beforeToHtml();
}

Above method sets product collection before html render.

Note: getProductCollection() and _getProductCollection() are not same. Both are completely different method.

2) $this->getDisplayType()

Any constant variable can be defined using const statement.

const DISPLAY_TYPE_NEW_PRODUCTS = 'new_products';

and that variable can be used as:

self::DISPLAY_TYPE_NEW_PRODUCTS;

So, self::DISPLAY_TYPE_NEW_PRODUCTS will return new_products.