使用linq查询从sql数据库表中获取数据

Question

我正在使用带有下拉菜单的自适应卡，我能够通过使用linq to sql将这些值动态获取到第一个下拉菜单中。现在基于我选择的第一个下拉菜单值，我希望填充第二个下拉列表值。我试过在数据库中有2个表，试图在两个表上执行联接操作以获得第二个下拉值，但是它没有用。

               var selectitem = (from each in db.maintabports select new { each.portname }).ToList();



            List<AdaptiveCards.Choice> list = new List<AdaptiveCards.Choice>();
            List<AdaptiveCards.Choice> list2 = new List<AdaptiveCards.Choice>();
            foreach (var item in selectitem)
            {
                AdaptiveCards.Choice choice = new AdaptiveCards.Choice()
                {

                    Title = item.portname,
                    Value = item.portname
                };

                list.Add(choice);
            }
            var selectitem1 = (from each in db.maintabports join t in db.projmen on each.Id equals t.Id    select new { t.projmanager });
            foreach (var item1 in selectitem1)
            {
                AdaptiveCards.Choice choice = new AdaptiveCards.Choice()
                {
                   Title=item1.projmanager,

                    Value = item1.projmanager
                };
                list2.Add(choice);


            }


            var card = new AdaptiveCard()
            {
                Body = new List<CardElement>()
{
    new TextBlock()
    {
        Color = TextColor.Attention,
        Weight = TextWeight.Bolder,
        Size = TextSize.Medium,
        Text = "Select a title",
    },
    new ChoiceSet()
    {
        Id = "title",
        Style = ChoiceInputStyle.Compact,
        IsRequired = false,
        IsMultiSelect = false,
        Value = "1",

        Choices =list
    },
     new ChoiceSet()
    {
        Id = "managernames",
        Style = ChoiceInputStyle.Compact,
        IsRequired = false,
        IsMultiSelect = false,
        Value = "1",

        Choices =list2
    },
},
   };