Is there a way to dinamically call a laravel relationship in this scenario?

I'm working on a Laravel project with a few models. My main model Product has a few many to many relationships with some secondary models on the app. I created the required methods to setup the relationships on the respective models, the thing is, that now I need a clean way to add or remove the related secondary models. Having my Product defined as:

class Product extends Model 
{

    public function equipments()
    {
        return $this->belongsToMany('App\Equipment', 'product_has_equipment');
    }

    public function rawmaterials()
    {
        return $this->belongsToMany('App\RawMaterial', 'product_has_raw_material')->withPivot('composition');
    }

    public function indirectcosts()
    {
        return $this->belongsToMany('App\IndirectCost', 'product_has_indirect_cost');
    }

    public function presentations()
    {
        return $this->belongsToMany('App\Presentation', 'product_has_presentation');
    }
}

I tried to do the following:

public function addRelated(string $type, array $items)
{
    $this->__call($type, [])->attach($items);
}

I thougth that way it would be possible to just specify a string matching one of the relationships names, and with __call it could be called dinamically, so if I pass 'equipments' as $type on the above function, I hoped the inner call would be:

$this->equipments()->attach($items);

But instead I got the error

This seems strange, given that the "undefined method" is exactly the same as the one adviced by laravel in same page.

Take into account that I DO know that this approach may be insecure code-wise, but this project will be an API running on a local server only to be consumed by an electron app, so security is not my priority in this case.

Solution

check the source code of Laravel model

/**
     * Handle dynamic method calls into the model.
     *
     * @param  string  $method
     * @param  array  $parameters
     * @return mixed
     */
    public function __call($method, $parameters)
    {
        if (in_array($method, ['increment', 'decrement'])) {
            return $this->$method(...$parameters);
        }

        return $this->forwardCallTo($this->newQuery(), $method, $parameters);
    }

and forwardCall says

/**
     * Forward a method call to the given object.
     *
     * @param  mixed  $object
     * @param  string  $method
     * @param  array  $parameters
     * @return mixed
     *
     * @throws \BadMethodCallException
     */
    protected function forwardCallTo($object, $method, $parameters)
    {
        try {
            return $object->{$method}(...$parameters);
        } catch (Error | BadMethodCallException $e) {
            $pattern = '~^Call to undefined method (?P<class>[^:]+)::(?P<method>[^\(]+)\(\)$~';

            if (! preg_match($pattern, $e->getMessage(), $matches)) {
                throw $e;
            }

            if ($matches['class'] != get_class($object) ||
                $matches['method'] != $method) {
                throw $e;
            }

            static::throwBadMethodCallException($method);
        }
    }

since the $this->newQuery() returns a Illuminate\Database\Eloquent\Builder;,which doesn't have wanted methods