ZendFramework transaction processing problems

An official example of ZendFramework transaction processing is provided as follows: & lt ;? Php // & nbsp; create an & nbsp; $ db object and start a transaction. $ db-& gt; beginTransaction (); // & nbsp; try database operations. // & nbsp; if successful, the com Zend Framework transaction processing problem
An official example is provided as follows:

 
// Create a $ db object and start a transaction.
$ Db-> beginTransaction ();

// Try database operations.
// If the operation succeeds, commit the operation;
// Assume that roll back.
Try {
$ Db-> query (...);
$ Db-> commit ();
} Catch (Exception $ e ){
$ Db-> rollBack ();
Echo $ e-> getMessage ();
}

?>

The instance I wrote does not pass, but prompts
Fatal error: Uncaught exception 'pdoexception' with message 'There is already an active transaction' in E: \ php \ ZendFramework \ library \ Zend \ Db \ Adapter \ Pdo \ Abstract. php: 305 Stack trace: #0 E: \ php \ ZendFramework \ library \ Zend \ Db \ Adapter \ Pdo \ Abstract. php (305): PDO-> beginTransaction () #1 E: \ php \ ZendFramework \ library \ Zend \ Db \ Adapter \ Abstract. php (484): Zend_Db_Adapter_Pdo_Abstract-> _ beginTransaction () #2 D: \ svnrepos \ WiClub \ src \ application \ models \ shop. php (76): Zend_Db_Adapter_Abstract-> beginTransaction () #3 D: \ svnrepos \ WiClub \ src \ application \ controllers \ ShopController. php (507): shop-> inserttest (Array) #4 E: \ php \ ZendFramework \ library \ Zend \ Controller \ Action. php (513): ShopController-> shopaddtestAction () #5 E: \ php \ ZendFramework \ library \ Zend \ Controller \ Dispatcher \ Standard. php (289): Zend_Controller_Action-> dispatch ('shopaddtestacti... ') #6 E: \ php \ ZendFramework \ library \ Zend \ Controller \ Front. php (946): Zend_Controller_Dispatcher_Standard-> dispatch (Object (Zend_Controller_Request_Http), Object (Zend_Controller_Response_Http) #7 D: \ svnrepos \ WiC in E: \ php \ ZendFramework \ library \ Zend \ Db \ Adapter \ Pdo \ Abstract. php on line 305

Seems to be prompting that a transaction is already running? I am not familiar with ZF just a moment ago. paste the relevant source file.

Config. ini

[general]
db.adapter = PDO_MYSQL
db.config.host = localhost
db.config.username = root
db.config.password = 123456
db.config.dbname = testdb 
db.config.charset = utf8
date_default_timezone = "PRC"

Util. php [the Common folder, which is the same as the controllers folder and models folder]

 require_once 'Zend/Config/Exception.php';
require_once 'Zend/Config/Ini.php';
require_once 'Zend/Registry.php';
require_once 'Zend/Db.php';
require_once 'Zend/Db/Table.php';
//require_once 'common/Blowfish.php';
//require_once 'common/Hosts.php';
class Common_Util
{
        public static function getDb($configName,$setcharset=false)
{
if($configName)
{
$config=new Zend_Config_Ini('../config.ini',$configName);
                        $registry= Zend_Registry::getInstance();
                        $registry->set('config',$config);
                        $params=$config->db->config->toArray();
                        $params['options']=array(PDO::ATTR_PERSISTENT => true);
                        $db = Zend_Db::factory($config->db->adapter,$params);