yii\db\Query::where PHP Method

    public function where($condition, $params = [])
    {
        $this->where = $condition;
        $this->addParams($params);
        return $this;
    }

 /**
  * Lists all Job models.
  * @return mixed
  */
 public function actionIndex()
 {
     $model = new Job();
     // This is used to search/filter organizations
     $dataProvider = null;
     if (isset($_GET['user_id'])) {
         $user_id = $_GET['user_id'];
         if ($user_id !== null) {
             $query = new Query();
             $query->from(Job::tableName());
             $query->where(['user_id' => $user_id]);
             $dataProvider = new ActiveDataProvider(['query' => $query, 'pagination' => ['pageSize' => 5]]);
         }
     } else {
         $dataProvider = new ActiveDataProvider(['query' => Job::find(), 'pagination' => ['pageSize' => 5]]);
     }
     if ($model->load(Yii::$app->request->post())) {
         $query = new Query();
         $query->from(Job::tableName());
         if (!is_null($model->employment_type) && is_array($model->employment_type)) {
             $query->where(['employment_type' => array_map('intval', $model->employment_type)]);
         }
         if (!is_null($model->job_type) && is_array($model->job_type)) {
             $query->where(['job_type' => array_map('intval', $model->job_type)]);
         }
         if (!is_null($model->work_domain) && is_array($model->work_domain)) {
             $query->andWhere(['work_domain' => array_map('intval', $model->work_domain)]);
         }
         if (isset($_GET['user_id'])) {
             $query->andWhere(['user_id' => $_GET['user_id']]);
         }
         $dataProvider = new ActiveDataProvider(['query' => $query, 'pagination' => ['pageSize' => 5]]);
     }
     return $this->render('index', ['model' => $model, 'dataProvider' => $dataProvider]);
 }