How to add more attributes to product collection

Question

It seems that many of the custom attributes that i've created aren't present in the product collection that i'm producing. How do I add more of them? This is the method I use to get the new product collection.

protected function _getProductCollection()
{
    $todayStartOfDayDate = Mage::app()->getLocale()->date()
        ->setTime('00:00:00')
        ->toString(Varien_Date::DATETIME_INTERNAL_FORMAT);
    $todayEndOfDayDate = Mage::app()->getLocale()->date()
        ->setTime('23:59:59')
        ->toString(Varien_Date::DATETIME_INTERNAL_FORMAT);
    /** @var $collection Mage_Catalog_Model_Resource_Product_Collection */
    //$collection = Mage::getModel('catalog/product')->getCollection()
    $collection = Mage::getResourceModel('catalog/product_collection');
    $collection->setVisibility(Mage::getSingleton('catalog/product_visibility')->getVisibleInCatalogIds());
    $collection = $this->_addProductAttributesAndPrices($collection)
        ->addStoreFilter()
        ->addAttributeToFilter('news_from_date', array('or' => array(
            0 => array('date' => true, 'to' => $todayEndOfDayDate),
            1 => array('is' => new Zend_Db_Expr('null')))
        ), 'left')
        ->addAttributeToFilter('news_to_date', array('or' => array(
            0 => array('date' => true, 'from' => $todayStartOfDayDate),
            1 => array('is' => new Zend_Db_Expr('null')))
        ), 'left')
        ->addAttributeToFilter(
            array(
                array('attribute' => 'news_from_date', 'is' => new Zend_Db_Expr('not null')),
                array('attribute' => 'news_to_date', 'is' => new Zend_Db_Expr('not null'))
            )
        )
        ->setPageSize($this->getProductsCount())
        ->setCurPage(1);
    return $collection;
}

The resultant __tostring() of the collection looks like this:

SELECT 1 AS status, e.entity_id, e.type_id, e.attribute_set_id, cat_index.position AS cat_index_position, price_index.price, price_index.tax_class_id, price_index.final_price, IF(price_index.tier_price IS NOT NULL, LEAST(price_index.min_price, price_index.tier_price), price_index.min_price) AS minimal_price, price_index.min_price, price_index.max_price, price_index.tier_price, e.name, e.short_description, e.price, e.special_price, e.special_from_date, e.special_to_date, e.small_image, e.thumbnail, e.news_from_date, e.news_to_date, e.url_key, e.required_options, e.image_label, e.small_image_label, e.thumbnail_label, e.msrp_enabled, e.msrp_display_actual_price_type, e.msrp, e.tax_class_id, e.price_type, e.weight_type, e.price_view, e.shipment_type, e.links_purchased_separately, e.links_exist, e.giftcard_amounts, e.allow_open_amount, e.open_amount_min, e.open_amount_max, e.entity_id, e.attribute_set_id, e.type_id, e.allow_open_amount, e.cost, e.created_at, e.email_template, e.enable_googlecheckout, e.giftcard_amounts, e.giftcard_type, e.gift_message_available, e.gift_wrapping_available, e.gift_wrapping_price, e.has_options, e.image_label, e.is_recurring, e.is_redeemable, e.lifetime, e.links_exist, e.links_purchased_separately, e.links_title, e.msrp, e.msrp_display_actual_price_type, e.msrp_enabled, e.name, e.news_from_date, e.news_to_date, e.open_amount_max, e.open_amount_min, e.price, e.price_type, e.price_view, e.recurring_profile, e.required_options, e.shipment_type, e.short_description, e.sku, e.sku_type, e.small_image, e.small_image_label, e.special_from_date, e.special_price, e.special_to_date, e.tax_class_id, e.thumbnail, e.thumbnail_label, e.updated_at, e.url_key, e.url_path, e.use_config_email_template, e.use_config_is_redeemable, e.use_config_lifetime, e.visibility, e.weight, e.weight_type FROM catalog_product_flat_1 AS e INNER JOIN catalog_category_product_index AS cat_index ON cat_index.product_id=e.entity_id AND cat_index.store_id='1' AND cat_index.visibility IN(2, 4) AND cat_index.category_id = '2' INNER JOIN catalog_product_index_price AS price_index ON price_index.entity_id = e.entity_id AND price_index.website_id = '1' AND price_index.customer_group_id = 0 WHERE (((((e.news_from_date <= '2015-02-04 23:59:59') OR (e.news_from_date IS null))))) AND (((((e.news_to_date >= '2015-02-04 00:00:00') OR (e.news_to_date IS null))))) AND ((e.news_from_date IS not null) OR (e.news_to_date IS not null))

Answer 1

You have 2 options here.

1. Use ->addAttributeToSelect(array('attr1', 'attr2', ...)). This should make your attributes be loaded in the collection and you have control on what you load.
2. You can edit the attributes you want in the list and set the flag use in product list to yes. Then rebuild the indexes. This is fast and requires no coding. the downside is the attributes will be loaded in every product list and might impact performance.