Singelton Collection Pattern #Magento

collection.php

<?php

class Zookal_Core_Helper_Data extends Mage_Core_Helper_Abstract
{
    private $_objectCache = [];

    public function getCollectionSingleton($modelClass, array $collectionOptions = null, $cacheKey = null)
    {
        $cacheKey = null === $cacheKey ? $modelClass . '/' . json_encode($collectionOptions) : (string)$cacheKey;
        // $cacheKey = md5($cacheKey); if preferred
        if (isset($this->_objectCache[$cacheKey])) {
            return $this->_objectCache[$cacheKey];
        }
        /** @var Varien_Data_Collection_Db $collection */
        $collection              = Mage::getResourceModel($modelClass);
        if(false === $collection) {
           return false;
        }
        $hasAddAttributeToFilter = method_exists($collection, 'addAttributeToFilter');
        if ($hasAddAttributeToFilter && isset($collectionOptions['atf'])) {
            foreach ($collectionOptions['atf'] as $attribute => $condition) {
                $collection->addAttributeToFilter($attribute, $condition);
            }
        }
        $hasAddAttributeToSelect = method_exists($collection, 'addAttributeToSelect');
        if ($hasAddAttributeToSelect && isset($collectionOptions['ats'])) {
            foreach ($collectionOptions['ats'] as $attribute) {
                $collection->addAttributeToSelect($attribute);
            }
        }
        $this->_objectCache[$cacheKey] = $collection;
        return $collection;
    }

    /**
     * @return Mage_Catalog_Model_Resource_Product_Collection
     */
    public function getProducts()
    {
        return $this->getCollectionSingleton('catalog/product_collection', [
            'atf' => ['sku', array('in' => 'ottoman')],
            'ats' => 'name',
        ]);
    }
}

collectionUpdate.php

<?php

class Zookal_Core_Helper_Data extends Mage_Core_Helper_Abstract
{
    private $_objectCache = [];

    /**
     * @param string $modelClass
     * @param array  $collectionOptions
     * @param null   $cacheKey
     *
     * @return bool|Varien_Data_Collection_Db
     */
    public function getCollectionSingleton($modelClass, array $collectionOptions = null, $cacheKey = null)
    {
        $cacheKey = null === $cacheKey ? $modelClass . '/' . json_encode($collectionOptions) : (string)$cacheKey;
        // $cacheKey = md5($cacheKey); if preferred
        if (isset($this->_objectCache[$cacheKey])) {
            return $this->_objectCache[$cacheKey];
        }
        /** @var Varien_Data_Collection_Db $collection */
        $collection = Mage::getResourceModel($modelClass);
        if (false === $collection) {
            return false;
        }

        foreach ($collectionOptions as $method => $arguments) {
            if (true === method_exists($collection, $method)d) {
                call_user_func_array([$collection, $method], $arguments);
            }
        }

        $this->_objectCache[$cacheKey] = $collection;
        return $collection;
    }

    /**
     * @return Mage_Catalog_Model_Resource_Product_Collection
     */
    public function getProducts()
    {
        return $this->getCollectionSingleton('catalog/product_collection', [
            'addAttributeToFilter' => ['sku', array('in' => 'ottoman')],
            'addAttributeToSelect' => ['name'],
        ]);
    }
}

Second implementation is more generic