Get read and write adapters in Magento

Get database read adapter

/* @var $adapter Varien_Db_Adapter_Interface */
$adapter = Mage::getSingleton('core/resource')
    ->getConnection('core_read');

Get database write adapter

/* @var $adapter Varien_Db_Adapter_Interface */
$adapter = Mage::getSingleton('core/resource')
    ->getConnection('core_write');