Zend表单和注释验证

我正在尝试使用注释来构建和验证zend表单。但目前我收到一个错误，当我打开showformAction:

"致命错误:未捕获的异常'Zend'Form' exception 'InvalidElementException'伴有消息'在表单中未找到名称为[username]的元素'…"

实体' User.php

namespace Application'Model;
use Zend'Form'Annotation;
/**
 * @Annotation'Hydrator("Zend'Stdlib'Hydrator'ObjectProperty")
 * @Annotation'Name("user")
 */
class User
{
    /**
     * @Annotation'Attributes({"type":"text" })
     * @Annotation'Validator({"type":"Regex","options":{"regex":"/^[a-zA-Z][a-zA-Z0-9_-]{1,19}/"}})
     * @Annotation'Options({"label":"Username:"})
     */
    public $username;
}

控制器' ProductsController.php

namespace Application'Controller;
use Zend'Mvc'Controller'AbstractActionController;
use Zend'Json'Json;
use Zend'View'Model'JsonModel;
use Zend'View'Model'ViewModel;
use Zend'Debug'Debug;
use Application'Entity'Products;
use Application'Entity'Category;
use Application'Form'ProductsForm;
use Doctrine'ORM'EntityManager;
use Application'Model'User;
use Zend'Form'Annotation'AnnotationBuilder;
class ProductsController extends AbstractActionController {
    protected $albumTable;
    protected $em;
    protected $form;
  public function savetodb($data) {
        //code save to db ....
    }
    protected function getForm() {
        $entity = new User();
        $builder = new AnnotationBuilder();
        $this->form = $builder->createForm($entity);
        return $this->form;
    }
    public function showformAction() {
        $viewmodel = new ViewModel();
        $form = $this->getForm();
        $request = $this->getRequest();
        //disable layout if request by Ajax
        $viewmodel->setTerminal($request->isXmlHttpRequest());
        $is_xmlhttprequest = 1;
        if (!$request->isXmlHttpRequest()) {
            //if NOT using Ajax
            $is_xmlhttprequest = 0;
            if ($request->isPost()) {
                $form->setData($request->getPost());
                if ($form->isValid()) {
                    //save to db <span class="wp-smiley emoji emoji-wink" title=";)">;)</span>
                    $this->savetodb($form->getData());
                }
            }
        }
        $viewmodel->setVariables(array(
            'form' => $form,
            // is_xmlhttprequest is needed for check this form is in modal dialog or not
            // in view
            'is_xmlhttprequest' => $is_xmlhttprequest
        ));
        return $viewmodel;
    }
    public function validatepostajaxAction() {
        $form = $this->getForm();
        $request = $this->getRequest();
        $response = $this->getResponse();
        $messages = array();
        if ($request->isPost()) {
            $form->setData($request->getPost());
            if (!$form->isValid()) {
                $errors = $form->getMessages();
                foreach ($errors as $key => $row) {
                    if (!empty($row) && $key != 'submit') {
                        foreach ($row as $keyer => $rower) {
                            //save error(s) per-element that
                            //needed by Javascript
                            $messages[$key][] = $rower;
                        }
                    }
                }
            }
            if (!empty($messages)) {
                $response->setContent('Zend'Json'Json::encode($messages));
            } else {
                //save to db <span class="wp-smiley emoji emoji-wink" title=";)">;)</span>
                $this->savetodb($form->getData());
                $response->setContent('Zend'Json'Json::encode(array('success' => 1)));
            }
        }
        return $response;
    }
}