Magento: where are catalog filter's (url get parameter's) handled in magento? and where is sql request made to fetch the result? - magento

Question

Magento currently handles only one filter parameter per category .
I want the filter to handle more than one parameter's for the same category.
eg, Suppose I choose 2 colors red and black in the filter using a checkbox for ex, and then click submit button (which I have added), then I want the page to display results for product's having color red or black.
For this, I want to know :
Where are GET parameter's for any filtering process handled in magento.
Where is the sql request made to fetch the results of filtering process.
So that I could handle more than one filter parameter's and display the results.
Any help or suggestion would be of great help.
Thanks in advance..

Answer 1

For your example scenario, you are filtering using attribute color having its attribute ID. The resource model is responsible to execute the SQL operations being performed on any attribute selection.
Go to file app/code/core/Mage/Catalog/Model/Resource/Layer/Filter/Attribute.php
public function applyFilterToCollection($filter, $value)
{
$collection = $filter->getLayer()->getProductCollection();
$attribute = $filter->getAttributeModel();
$connection = $this->_getReadAdapter();
$tableAlias = $attribute->getAttributeCode() . '_idx';
$conditions = array(
"{$tableAlias}.entity_id = e.entity_id",
$connection->quoteInto("{$tableAlias}.attribute_id = ?", $attribute->getAttributeId()),
$connection->quoteInto("{$tableAlias}.store_id = ?", $collection->getStoreId()),
$connection->quoteInto("{$tableAlias}.value = ?", $value)
);
$collection->getSelect()->join(
array($tableAlias => $this->getMainTable()),
implode(' AND ', $conditions),
array()
);
return $this;
}
In the above function, when you print the collection and exit it before return using,
$collection->printlogquery(true);
you will see the SQL query generated to fetch the results of filtering process.
You can modify this resource model in your local and using INNER JOIN change the SQL query to work for multiple attribute values.