Zend表单提交错误

我的代码遇到问题，我试图提交表单以填写数据库并将我重定向到我的索引页面，但是当我发送表单时，我不断收到此错误：

消息：SQLSTATE[23000]：完整性约束冲突：1048 列"Number_of_employees"不能为空

这是我对AddForm，模型和Form的索引

//Index
      public function addform3Action()
    {
         $form = new Application_Form_CompanyDescription();

        $this->view->form = $form;
        if ($this->getRequest()->isPost()) {
            $formData = $this->getRequest()->getPost();
            if ($form->isValid($formData)) {                
                $Number_of_employees = $form->getValue('Number of employees');
                $Organisation_type = $form->getValue('$Organisation type');
                $Annual_Turnover = $form->getValue('Annual Turnover');
                $Organisation_Registration_Number = $form->getValue('Organisation Registration Number');
                $Vat_Registrtion_Number = $form->getValue('VatRegistrtion Number');
                $Income_Tax_Reference_Number = $form->getValue('Income Tax Reference Number');
                $Tax_Clearance_Certificate= $form->getValue('Tax Clearance Certificate');
                $Tax_Clearance_Certificate_ExpiryDate = $form->getValue('Tax Clearance Certificate ExpiryDate');
                $Commenced_Trading_Date = $form->getValue('Commenced Trading Date');    
                $BBBEE_Scorecard= $form->getValue('BBBEE Scorecard');
                $Rating_Agency = $form->getValue('Rating Agency');
                $Rating_Expiry_Date = $form->getValue('Rating Expiry Date');                            

                $companydescription= new Application_Model_DbTable_CompanyDescription();
                $companydescription->addform3CompanyDescription($Number_of_employees, $Organisation_type, $Annual_Turnover, $Organisation_Registration_Number, $Vat_Registrtion_Number, $Income_Tax_Reference_Number, $Tax_Clearance_Certificate, $Tax_Clearance_Certificate_ExpiryDate, $Commenced_Trading_Date, $BBBEE_Scorecard, $Rating_Agency, $Rating_Expiry_Date);

                $this->_helper->redirector('index');
            } else {
                $form->populate($formData);
            }
        }
    }

}  
//model
<?php
class Application_Model_DbTable_CompanyDescription extends Zend_Db_Table_Abstract
{
    protected $_name = 'companydescription';

        public function getCompanyDescription($id)
    {
        $id = (int)$id;
        $row = $this->fetchRow('id = ' . $id);
        if (!$row) {
        throw new Exception("Could not find row $id");
        }
        return $row->toArray();
    }
    public function addform3CompanyDescription($Number_of_employees, $Organisation_type, $Annual_Turnover, $Organisation_Registration_Number, $Vat_Registrtion_Number, $Income_Tax_Reference_Number, $Tax_Clearance_Certificate, $Tax_Clearance_Certificate_ExpiryDate, $Commenced_Trading_Date, $BBBEE_Scorecard, $Rating_Agency, $Rating_Expiry_Date)
    {
        $data = array(
            'Number_of_employees'=> $Number_of_employees,
            'Organisation_type'=> $Organisation_type,
            'Annual_Turnover'=> $Annual_Turnover,
            'Organisation_Registration_Number'=> $Organisation_Registration_Number,
            'Vat_Registrtion_Number'=> $Vat_Registrtion_Number,
            'Income_Tax_Reference_Number'=> $Income_Tax_Reference_Number,
            'Tax_Clearance_Certificate'=> $Tax_Clearance_Certificate,
            'Tax_Clearance_Certificate_ExpiryDate'=> $Tax_Clearance_Certificate_ExpiryDate,
            'Commenced_Trading_Date'=> $Commenced_Trading_Date,
            'BBBEE_Scorecard'=> $BBBEE_Scorecard,
            'Rating_Agency'=> $Rating_Agency,
            'Rating_Expiry_Date'=> $Rating_Expiry_Date,
        );
        $this->insert($data);
    }

}
//aform for addform3
<?php
class Application_Form_CompanyDescription extends Zend_Form
{
    public function init()
    {
        $this->setName('companydescription');
        $id = new Zend_Form_Element_Hidden('id');
        $id->addFilter('Int');
        $Number_of_employees = new Zend_Form_Element_Text('Number of employees');
        $Number_of_employees->setLabel('Number of employees')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Organisation_type = new Zend_Form_Element_Text('Organisation type');
        $Organisation_type->setLabel('Organisation type')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('NotEmpty');
        $Annual_Turnover = new Zend_Form_Element_Text('Annual Turnover');
        $Annual_Turnover->setLabel('Annual Turnover')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Organisation_Registration_Number = new Zend_Form_Element_Text('Organisation Registration Number');
        $Organisation_Registration_Number->setLabel('Organisation Registration Number')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Vat_Registrtion_Number = new Zend_Form_Element_Text('Vat Registrtion Number');
        $Vat_Registrtion_Number->setLabel('Vat Registrtion Number')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Income_Tax_Reference_Number= new Zend_Form_Element_Text('Income Tax Reference Number');
        $Income_Tax_Reference_Number->setLabel('Income Tax Reference Number')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Tax_Clearance_Certificate = new Zend_Form_Element_Text('Tax Clearance Certificate');
        $Tax_Clearance_Certificate->setLabel('Tax Clearance Certificate')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Tax_Clearance_Certificate_ExpiryDate = new Zend_Form_Element_Text('Tax Clearance Certificate ExpiryDate');
        $Tax_Clearance_Certificate_ExpiryDate->setLabel('Tax Clearance Certificate ExpiryDate')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Commenced_Trading_Date = new Zend_Form_Element_Text('Commenced Trading Date');
        $Commenced_Trading_Date->setLabel('Commenced Trading Date')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $BBBEE_Scorecard = new Zend_Form_Element_Text('BBBEE Scorecard');
        $BBBEE_Scorecard->setLabel('BBBEE Scorecard')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');
        $Rating_Agency = new Zend_Form_Element_Text('Rating Agency');
        $Rating_Agency->setLabel('Rating Agency')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('NotEmpty');

        $Rating_Expiry_Date = new Zend_Form_Element_Text('Rating Expiry Date');
        $Rating_Expiry_Date->setLabel('Rating Expiry Date')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('Digits');


        $submit = new Zend_Form_Element_Submit('submit');
        $submit->setLabel('Next');
        $submit->setAttrib('id', 'submitbutton');
        $this->addElements(array($id, $Number_of_employees, $Organisation_type, $Annual_Turnover, $Organisation_Registration_Number, $Vat_Registrtion_Number, $Income_Tax_Reference_Number, $Tax_Clearance_Certificate, $Tax_Clearance_Certificate_ExpiryDate, $Commenced_Trading_Date, $BBBEE_Scorecard, $Rating_Agency, $Rating_Expiry_Date, $submit));
    }

}