Many to Many relation how to override?

[lgt]

I try to override the base controllers postNew() method in my custom Controller like assigning many to many relationship but I get error

Call to undefined method Illuminate\Database\Query\Builder::sync()

the overrided looks like

public function postNew() {

    $record = $this->model->getNew(Input::all());
    $record->campaign_title= Input::get('campaign_title');

    $valid = $this->validateWithInput === true ? $record->isValid(Input::all()) : $record->isValid();

    if (!$valid)
        return Redirect::to('admin/' . $this->new_url)->with('errors', $record->getErrors())->withInput();

    // Run the hydration method that populates anything else that is required / runs any other
    // model interactions and save it.
    $record->save();

    $record->networks()->sync([3,4]);

    // Redirect that shit man! You did good! Validated and saved, man mum would be proud!
    return Redirect::to($this->object_url)->with('success', new MessageBag(array('Item Created')));
}

In my repositiry I have a networks method()

public function networks()
{
    return $this->belongsToMany('Network', 'campaign_networks_relationhsips');
}

So how to extend the base eloquent to can hydrate tables?