函数loadModel（）返回“新记录”

I have the following code for actionUpdate:

public function actionUpdate($id)
{

    $model=$this->loadModel($id);

    // Uncomment the following line if AJAX validation is needed
    //$this->performAjaxValidation($model);

    echo $model->isNewRecord;

    if(isset($_POST['Program']))
    {
        $model->attributes = $_POST['Program'];

        if($model->save()){

            $this->redirect(array('admin'));
        }
    }

    $this->render('update',array(
        'model'=>$model,
    ));
}

The echo $model->isNewRecord returns TRUE but the model is not empty. I have an existing model with the given id and the attributes matched the model, so when I call $model->save() it gives me

CDbException CDbCommand failed to execute the SQL statement: Duplicate entry for key 'PRIMARY'.

I can't find the reason why it is considered as a new record.

Thanks in advance!

Edit:

Here's the code for my loadModel() function:

public function loadModel($id)
{

    $model=Program::model()->findByPk($id);
    if($model===null)
        throw new CHttpException(404,'The requested page does not exist.');
    return $model;
}

CActiveRecord performs the isNewRecord test only after performing afterSave().

So at that point in your code $model->isNewRecord was not tested yet.

Maybe in your situation, it is better to set your own flag (or model attribute), since you anyway know that it is not a new record at that point in your code.