Laravel form doesn't update values in database instead is delete them

I have form where I can change user role. When I try to change and hit Save button I've got invalid foreach() argument error and previous record in database for this user is deleted completely.

This is my form

{!! Form::model($user, ['method' => 'PATCH','route' => ['admin.addper', $user->user_id]]) !!}
<div class="row">
    <div class="col-md-4 col-xs-12">
         <div class="form-group">
             <label for="title" class="control-block">Username:</label>
                
         </div>
    </div><!-- end col-4/12 -->
    <div class="col-xs-12 col-md-8">
         <div class="form-group">
            <label for="title" class="control-block">Choose which Role you want to assign to user:</label><br>
                @foreach($roles as $value)
                    
                        <strong></strong> 
                        <br/>
                @endforeach
         </div>
    </div>
    <div class="col-xs-12 col-sm-12 col-md-12 text-center">
            <button type="submit" class="btn btn-primary">Submit</button>
    </div>
</div>
{!! Form::close() !!}

And this is the controller part

public function update(Request $request, $id)
{
    $this->validate($request, [
        'roles' => 'required'
    ]);

    $input = $request->all();
    $user = User::find($id);
    $user->update($input);
    DB::table('role_user')->where('user_id',$id)->delete();

    foreach ($request->input('roles') as $key => $value) {
        $user->attachRole($value);
    }

    return redirect()->route('users')
                    ->with('success','User Role Updated Successfully');
}

The error is on the foreach in the controller

ErrorException: Invalid argument supplied for foreach()

Since I'm sure that I pass correct user_id and correct value of role_id why is this error?

dd($request->input('roles'));

return correct id which I'm choose on checkbox.

via Chebli Mohamed