<?= $form->field($model, 'maincatalog')->dropDownList($maincatalog, ["prompt" => Yii::t('app', 'select_cat')])->label(false) ?>

<?= $form->field($model, 'listproduct')->dropDownList($listproduct, ["prompt" => Yii::t('app', 'select_cat')])->label(false) ?>

<?= $form->field($model, 'q')->textInput(['class' => 'input'])->label('')?>


$query = Addproduct::find()
                     ->where(['catalog' => $maincatalog])
                     ->andWhere(['product' => $listproduct])
                     ->andWhere(['like', 'titleru', $q])->all();

$query = Addproduct::find();

if ($maincatalog != NULL)
    $query->where(['catalog' => $maincatalog]);

if ($listproduct != NULL)
    $query->andWhere(['product' => $listproduct]);


$query->andWhere(['like', 'titleru', $q])->all();

if($maincatalog == "" && $listproduct == "" && $q == ""){
  $query = "all empty";
} elseif($maincatalog == "" && $listproduct != "" && $q == ""){
  $query = Addproduct::find()->where(['product' => $listproduct])
    ->andWhere(['like', 'titleru', $q])->all();
} elseif($maincatalog != "" && $listproduct == "" && $q == "") {
  $query = Addproduct::find()->where(['catalog' => $maincatalog])
    ->andWhere(['like', 'titleru', $q])->all();
} elseif($maincatalog == "" && $listproduct == "" && $q != "") {
    $query = Addproduct::find()->where(['like', 'titleru', $q])->all();
} elseif($maincatalog == "" && $listproduct != "" && $q != "") {
    $query = Addproduct::find()->where(['product' => $listproduct])
       ->andWhere(['like', 'titleru', $q])->all();
} elseif($maincatalog != "" && $listproduct == "" && $q != "") {
   $query = Addproduct::find()->where(['catalog' => $maincatalog])
      ->andWhere(['like', 'titleru', $q])->all();
} else {
    $query = Addproduct::find()->where(['catalog' => $maincatalog])
     ->andWhere(['product' => $listproduct])->andWhere(['like', 'titleru', $q])->all();
}

$query = Addproduct::find();

    if ( $maincatalog != NULL )
        $query->where(['catalog' => $maincatalog]);


    $query->andWhere(['product' => $listproduct])
          ->andWhere(['like', 'titleru', $q])->all();

if($maincatalog == "" && $listproduct == "" && $q == ""){
$query = "all empty";
} elseif($maincatalog == "" && $listproduct != "" && $q == ""){
 $query = Addproduct::find()->where(['product' => $listproduct])-          >andWhere(['like', 'titleru', $q])->all();
} elseif($maincatalog != "" && $listproduct == "" && $q == "") {
$query = Addproduct::find()->where(['catalog' => $maincatalog])-    >andWhere(['like', 'titleru', $q])->all();
} elseif($maincatalog == "" && $listproduct == "" && $q != "") {
    $query = Addproduct::find()->where(['like', 'titleru', $q])->all();
} elseif($maincatalog == "" && $listproduct != "" && $q != "") {
$query = Addproduct::find()->where(['product' => $listproduct])->andWhere(['like', 'titleru', $q])->all();
} elseif($maincatalog != "" && $listproduct == "" && $q != "") {
    $query = Addproduct::find()->where(['catalog' => $maincatalog])-    >andWhere(['like', 'titleru', $q])->all();
} else {
    $query = Addproduct::find()->where(['catalog' => $maincatalog])-    >andWhere(['product' => $listproduct])->andWhere(['like', 'titleru', $q])-    >all();
}

$query = Addproduct::find();

    if ($maincatalog != NULL)
        $query->where(['catalog' => $maincatalog]);

    if ($listproduct != NULL)
        $query->andWhere(['product' => $listproduct]);


    $query->andWhere(['like', 'titleru', $q])->all();

$query = Addproduct::find()->where('***');

$query->andFilterWhere(['catalog' => $maincatalog]);

$query->all();

public  $q;
public  $listproduct;
public  $maincatalog;

public function rules()
{
    return [
        ['q', 'string'],
        ['listproduct', 'string'],
        ['maincatalog', 'string']
    ];
}