Q:

How to access Model in Controller in zend framework?

I am trying to call model methods from controller. but I am getting Fatal error: Class 'GuestModel' not found in.  error
following is the code ::
Controller ::
class GuestController extends Zend_Controller_Action
 {

     public function indexAction(){
        $guestbook = new GuestModel();
        $this->view->entries = $guestbook->fetchAll();
     }
 }

Model::
class GuestModel extends Zend_Db_Table_Abstract
 {
 public function fetchAll()
    {
        $resultSet = $this->getDbTable()->fetchAll();
        $entries   = array();
        foreach ($resultSet as $row) {
            $entry = new Application_Model_Guestbook();
            $entry->setId($row->id)
                  ->setEmail($row->email)
                  ->setComment($row->comment)
                  ->setCreated($row->created);
            $entries[] = $entry;
        }
        return $entries;
    }

    public function getDbTable()
    {
        if (null === $this->_dbTable) {
            $this->setDbTable('Application_Model_DbTable_Guestbook');
        }
        return $this->_dbTable;
    }

 public function setDbTable($dbTable)
    {
        if (is_string($dbTable)) {
            $dbTable = new $dbTable();
        }
        if (!$dbTable instanceof Zend_Db_Table_Abstract) {
            throw new Exception('Invalid table data gateway provided');
        }
        $this->_dbTable = $dbTable;
        return $this;
    }
 }

A:

Zend Framework autoload depends on using the correct directory structure and file naming conventions to find the classes automagically, from the looks of your code my guess would be you're not following it.
I see 2 possible solutions for your problem:

If possible, rename your class to Application_Model_Guestbook, the file to Guestbook.php and make sure to move it to your application/models/ directory. Then you just need to call it in your controller as $guestbook = new Application_Model_Guestbook();. Check this documentation example;
Create your own additional autoloading rules. Check the official documentation regarding Resource Autoloading. 

