magento, help to understand default product Template code

Question

I am a novice in magento but am trying to learn it in the least possible time. I Was going through: http://alanstorm.com/layouts_blocks_and_templates which says:

File: app/design/frontend/base/default/template/catalog/product/list.phtml contains :

<?php $_productCollection=$this->getLoadedProductCollection() ?>    <?php if(!$_productCollection->count()): ?> <div class="note-msg">
    <?php echo $this->__("There are no products matching the selection.") ?>    </div>
<?php else: ?>

The getLoadedProductCollection method can be found in the Template’s Block, Mage_Catalog_Block_Product_List ... and from there:

File: app/code/core/Mage/Catalog/Block/Product/List.php

...
public function getLoadedProductCollection()
{
    return $this->_getProductCollection();
}   
...

After that , the aforementioned page writes : The block’s _getProductCollection then instantiates models and reads their data, returning a result to the template.

I am just at a loss here. _getProductCollection() has this line:

 if (is_null($this->_productCollection))

1) Does _productCollection mean the protected variable $_productCollection ?

 if (is_null($this->_productCollection)) {
            $layer = $this->getLayer();

2) What is the explanation of $layer = $this->getLayer() plz?

After that I get:

 if ($this->getShowRootCategory()) {
                $this->setCategoryId(Mage::app()->getStore()->getRootCategoryId());
            }

3) Where is the method getShowRootCategory() ?

4)What approach can help me understand the pros and cons of the line :

$this->setCategoryId(Mage::app()->getStore()->getRootCategoryId());

5) My questions may sound so easy to many. But can you refer to any online resource to learn all these things and others as a beginner of magento?

Good Luck

Anton S Anton S · Accepted Answer · 2011-09-23T11:58:42

This if (is_null($this->_productCollection)) is a caching technique that is common to OOP code as methods cache their variables in object context and if the methods are called multiple times against same object or within the same object then it delivers the cached variable instead of asking it all over from database again.

you can answer your other questions by grepping the codebase or finding the methods you are curious about from source code. Sometimes a method is a magic method (set, get) and you won't find a method definition behind that

grep ' getRootCategoryId' app/code/ -rsn
app/code/core/Mage/Core/Model/Store/Group.php:275:    public function getRootCategoryId()
app/code/core/Mage/Core/Model/Store.php:850:    public function getRootCategoryId()

and the very basic grep patterns to use are:

use [space]methodname( to find the methods and where they are defined in codebase
use >methodname( to find where this method is called in codebase
use >setMethodName( to find where magic methods are set if you wonder why there is no definition for getSomeVariable() in your codebase

magento, help to understand default product Template code

2 Answers