Yii ActiveRecord save, little brother after I execute, why do I add a column to the database, but no data

Yii ActiveRecord Save, why do I add a column in the database, but no data?
Environment: Windows Ten + Wampservice + Yii2.0.6
Development tools: Phpstorm 9.0.2

Yii ActiveRecord Save, why do I add a column in the database, but no data?
What's the Official Handbook, why so many questions? Did I try a few, or did I say something wrong?
I built a model.
namespace App\models;
Use Yii\db\activerecord;
Class User extends ActiveRecord
{
public $username;
Public $password;

public static function model ($className =__class__)
{
Return Parent::model ($className);
}

public static function TableName ()
{
Return ' {{user}} ';
}
executing in the controller
$user = new User ();
$user->username = ' Hello ';
$user->password = ' world ';
$user->save ();
The database adds a column, but username and password are empty, only the previous ID, which I wrote in the database schema.
ID Int (TEN) unsigned NOT null primary key auto_increment.
executed in the browser
Localhost:80/yii/web/index.php?r=index/create execute without error, but view the database, add a column, but username and password are blank.
What should I do if I encounter this problem?
------to solve the idea----------------------
Print SQL to see the syntax for insert into, and also to check the structure of the table below.
------to solve the idea----------------------
If you encounter such debugging problems, you should first use Print_r ($user) to see if the $user is the result you want, and if the Public property field is correct, you should check that it is exactly the same as the table name in the database.

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