How to apply filter to magento model before loading or selecting the item?

Question

I am a newbie in magento development and want to implement softdelete on my models . So basically I have added a is_deleted field in tables. So when I delete any record I just set is_deleted to 1. Now my question is that if I select record(s) from either model or resource Model only filtered record where is_deleted is 0 should come. For Exmaple - $model->load($id) should return the record which is not soft deleted. Thanks for the help in advance

Answer 1

In your model you would need to override Mage_Core_Model_Abstract::load() function.

If the soft delete is on all models you need to override: Mage_Core_Model_Resource_Db_Abstract::load() method to something like:

public function load(Mage_Core_Model_Abstract $object, $value, $field = null)
{
    if (is_null($field)) {
        $field = $this->getIdFieldName();
    }

    $read = $this->_getReadAdapter();
    if ($read && !is_null($value)) {
        $select = $this->_getLoadSelect($field, $value, $object);
        $data = $read->fetchRow($select);

        if ($data && $data[is_delete] != 1) {
            $object->setData($data);
        }
    }

    $this->unserializeFields($object);
    $this->_afterLoad($object);

    return $this;
}

Here is how you could override an abstract class in Magento: https://stackoverflow.com/questions/15739628/override-extend-magento-abstract-class

Answer 2

$model = Mage::getModel('modulename/modelname')->getCollection()
         ->addFieldToFilter('is_deleted',0);

this code give a query like this

select * from yourtablename where (is_deleted= '0')

This $model will return only that data where is_deleted = 0