Laravel 5.1 I cant update model $user

I have this function where I want to update user background image so I write:

public function updateBg(Request $request)
    {
        $user = Auth::user();
        $this->validate($request, [
            'background' => 'image|max:10000',
            // validate also other fields here
        ]);
        // checking file is valid.
        if (!$request->file('background')->isValid()) return redirect()->back()->withErrors(["background" => "File is corrupt"]);

        // file is valid
        $destinationPath = public_path().'/images/Custaccounts/'.$user->id; // upload path
        $extension = $request->file('background')->getClientOriginalExtension(); // getting image extension
        $ran = str_random(5);
        $photo  = $ran.'.'.$extension;

        $request->file('background')->move($destinationPath, $photo); // uploading file to given path

        $bg = $user->id.'/'.$photo;
dd($bg);
        $user->update(['background' => $bg]);

        return Redirect::back();

            }

this line wont work: $user->update(['background' => $bg]); dd($bg) give me right string and image is uploaded just I cant update my 'background; field ...

also when I write:

    $user->update(['background' => $bg, 'name'=>'John']);

name is updated but background not... at user model background field is fillable of cource

via Chebli Mohamed