c# - 如何将 DBNull 检查到 linq 或 int32？

Question

我想获取 CategoryId 为 null 的所有行。我写了下面的代码，但它给了我错误

" Operator ' == ' can not applied to operands of type 'int?' and System.DBNull

   public Nullable<Int32>  CategoryId { get; set; }
    Game objGame;
    var query = (from gametypebygametype in db.GameByGameTypes.Where(x => x.CategoryId == DBNull.Value)
                  join game in db.Games
                 on gametypebygametype.GameId equals game.GameId into joined
    from game in joined.DefaultIfEmpty()
                              select new
                                 {
                                     game.GameId,
                                     game.GameName
                                 }
                                ).Distinct();
                    List<Game> objlistGame = new List<Game>();
                    foreach (var item_temp in query)
                    {
                        objGame = new Game();
                        objGame.GameId = item_temp.GameId;
                        objGame.GameName = item_temp.GameName;
                        objlistGame.Add(objGame);
                    }

Answer 1

尝试只使用 null 而不是 DBNull.Value 或 HasValue = false。