yii2-save-relations-behavior/tests/models/User.php

<?php

namespace tests\models;

class User extends \yii\db\ActiveRecord
{
    /**
     * @inheritdoc
     */
    public static function tableName()
    {
        return 'user';
    }

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            ['username', 'required'],
            ['username', 'unique', 'targetClass' => '\tests\models\User'],
        ];
    }

}