Updating pivot table by id in laravel

bookmaker table
id
name


bookmaker_user table
id 
account_name
bookmaker_id
user_id


user table
id
name

User Model :
public function bookmakers(){
    return $this->belongsToMany('Bookmaker', 'bookmaker_user', 'user_id', 'bookmaker_id')
            ->withPivot('id', 'accountname')->withTimestamps();
}


BookmakerController.php
public function update($id)
{
            $bookname = Input::get('booknamemodifselect');
            $accountname = Input::get('accountnamemodifinput');
            $bankrollinvested = Input::get('bankrollinvestedmodifinput');
            $bonus = Input::get('bonusmodifinput');
            $bankrollamount = Input::get('bankrollamountmodifinput');

            $bookmodif = DB::table('bookmakers')->where('name', $bookname)->first();


            $bookmaker = $this->user->bookmakers()->where('bookmaker_user.id','=',$id)->first();
            $bookmaker->pivot->bookmaker_id = $bookmodif->id;
            $bookmaker->pivot->save();
    }

$id is the id of the account

$this->user is the user authentified.

I want to update the bookmaker for an account by his id (by account id I mean) that belongs to the user auth. Because the user auth have multiple entries with the same bookmaker but different account name. It says 'Trying to get property of non-object'.

Solution

To sum up the comments below the question, it isn't a very common database design. And this also means, that it would probably be a good idea to change that. By converting the bookmaker_user pivot table into a full grown table with its own model class. Reasons for that are:

Multiple records that belong to the same user and bookmaker (many-to-many should only have one)
Additional data stored in the pivot table (while normally okay, it adds to the first point)
Easier handling of changes (e.g. changing the bookmaker of an account)

But that's not really the problem the question poses so here's that:

I tried it out locally and I didn't get any errors, but I wouldn't save to the database.
It seems to be some kind of bug or unexpected behavior. However a workaround is using the Query Builder.
In my opinion its even more elegant for this case...

$bookmodif = DB::table('bookmakers')->where('name', $bookname)->first();

if($bookmodif !== null){  // just to make sure the bookmaker exists
    DB::table('bookmaker_user')
        ->where('id', $id)
        ->update(array('bookmaker_id' => $bookmodif->id);
}