Why is the method and class not found not called?

Question

Yii

When calling a static method, it throws an error: "call_user_func() expects parameter 1 to be a valid callback, class 'BA::class' not found". Why doesn't call_user_func work and why is 'BA::class' not found? If the namespace of the model where the getProduct() method is the same common\models as the model (any models that are twitched by the getProduct method will and have the same namespace) is 'BA::class' .

public function getProduct() {
        $category = Category::findOne($this->category_id);

        if(!is_null($category->parent_id)) {
            $category = Category::findOne($category->parent_id);
        }

        $model = $category->title;

        if(count($model = explode(' ', $model)) > 1) {
            for($i = 0; count($model) > $i; $i++) {
                $model[$i] = ucfirst($model[$i]);
            }
            $model = implode($model, '');
        } else {
            $model = ucfirst($model[0]);
        }

        $model = $model.'::class';
        $model = call_user_func(model);

        return $this->hasOne($model, ['id' => 'product_id']);

Answer 1

Calling a static class method is done by passing an array as the first argument
call_user_func(array('MyClass', 'myCallbackMethod'));