LOCK每个日期只允许一条记录

Here's my current code

这是我目前的代码

[HttpPost]
    public void AddMenuItem(DateTime MenuDate, string MenuItemIds_String)
    {
        if (string.IsNullOrEmpty(MenuItemIds_String)) { return; }
        var MenuItemIds = MenuItemIds_String.Split(',').Select(x=>int.Parse(x));

        int JamaatId = 1;

        object thisLcok = new object();
        lock (thisLcok)
        {
            bool ParentPresent = db.DailyMenus.SingleOrDefault(x => x.JamaatId == JamaatId && x.MenuDate == MenuDate) != null;
            if (!ParentPresent)
            {
                db.DailyMenus.Add(new DailyMenu { JamaatId = JamaatId, MenuDate = MenuDate, MenuNoteText = string.Empty });
                db.SaveChanges();
            }
        }
        DailyMenu parentMenu = db.DailyMenus.Single(x => x.JamaatId == JamaatId && x.MenuDate == MenuDate);

        foreach(int id in MenuItemIds){
            bool AlreadyExits = parentMenu.DailyMenuItems.SingleOrDefault(x => x.MenuItem == db.MenuItems.Find(id)) != null;
            if (!AlreadyExits)
            {
                db.DailyMenuItems.Add(new DailyMenuItem { MenuItem = db.MenuItems.Find(id), DailyMenu = parentMenu });
                db.SaveChanges();
            }
        }
    }
[HttpPost]