Laravel 同步错误

I am running the following code,

if( $organisation->save() ) {

        if(isset($members)) {
            $organisation->users()->sync($members);
        }

        if(isset($teams)) {
            $organisation->teams()->sync($teams);
        }

        if(isset($teams)) {
            $organisation->clients()->sync($clients);
        }

        if(isset($projects)) {
            $organisation->projects()->sync($projects);
        }

        $organisation->load('users');
        $organisation->load('teams');
        $organisation->load('clients');
        $organisation->load('projects');

        return Response::make($organisation, 200);

    }

I am am getting the following error when I try and sync $projects,

数组看起来像这样，

[0] => 6 so a very very simple array. My relationships in the models look like this,

Organisation

public function projects()
{
    return $this->hasMany('Project');
}

Projects

public function organisations()
{
    return $this->belongsToMany('Organisation', 'organisation_id');
}

正如你所见，一个组织可以有很多项目.我看不出为什么会出现以下错误，

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