Yii framework Invalid datetime format on create - php

Question

I have such projects table structure
CREATE TABLE IF NOT EXISTS `projects` (
`project_id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(255) NOT NULL,
`description` text NOT NULL,
`url` varchar(255) NOT NULL,
`create_time` datetime DEFAULT NULL,
`create_user_id` int(11) DEFAULT NULL,
`update_time` datetime DEFAULT NULL,
`update_user_id` int(11) DEFAULT NULL,
PRIMARY KEY (`project_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;
when I try to create new record with next form
Rules in model:
public function rules()
{
// NOTE: you should only define rules for those attributes that
// will receive user inputs.
return array(
array('title, description, url', 'required'),
array('create_user_id, update_user_id', 'numerical', 'integerOnly'=>true),
array('title, url', 'length', 'max'=>255),
array('create_time, update_time', 'safe'),
// The following rule is used by search().
// Please remove those attributes that should not be searched.
array('project_id, title, description, url, create_time, create_user_id, update_time, update_user_id', 'safe', 'on'=>'search'),
);
}
I have received error
CDbCommand failed to execute the SQL statement: SQLSTATE[22007]:
Invalid datetime format: 1292 Incorrect datetime value: '' for column
'create_time' at row 1. The SQL statement executed was: INSERT INTO
projects (title, description, url, create_time,
create_user_id, update_time, update_user_id) VALUES (:yp0, :yp1,
:yp2, :yp3, :yp4, :yp5, :yp6)
Why? How can I tell Yii that datetime fields are not required and can contain default value if not entered.

Answer 1

Try this, and as this is self contained behavior inside Yii itself, it should work :
In the Rules model add this :
public function behaviors(){
return array('CTimestampBehavior'=>array(
'class' => 'zii.behaviors.CTimestampBehavior',
'createAttribute' => 'create_time',
'updateAttribute' => 'update_time',
'setUpdateOnCreate' => true,
));
}

Answer 2

U may try something like this after u click on the button Create it gets to some action
Take it for example actionCreate()
In actionCreate u do like as shown
public function actionCreate()
{
$model=new Project;
if(isset($_POST['Project']))
{
$model->attributes=$_POST['Project'];
$model->create_time=new CDbExpression('NOW()');
$model->save(false);
$this->redirect(array('view','id'=>$model->id));
}
$this->render('create',array(
'model'=>$model,
));
}

Answer 3

doesn't this work?
public function beforeSave()
{
if($this->isNewRecord)
{
$this->create_time=null;
$this->update_time=null;
}
return parent::beforeSave();
}