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

<?php

namespace tests\models;

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

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            [['project_id', 'user_id'], 'required'],
            [['project_id', 'user_id'], 'integer']
        ];
    }

}