Eloquent - where not equal to

Use where with a != operator in combination with whereNull

Code::where('to_be_used_by_user_id', '!=' , 2)->orWhereNull('to_be_used_by_user_id')->get()

For where field not empty this worked for me:

->where('table_name.field_name', '<>', '')

While this seems to work

Code::query()
    ->where('to_be_used_by_user_id', '!=' , 2)
    ->orWhereNull('to_be_used_by_user_id')
    ->get();

you should not use it for big tables, because as a general rule "or" in your where clause is stopping query to use index. You are going from "Key lookup" to "full table scan"

Instead, try Union

$first = Code::whereNull('to_be_used_by_user_id');

$code = Code::where('to_be_used_by_user_id', '!=' , 2)
        ->union($first)
        ->get();