使用Linq to Entities在winforms应用程序中调用组合框，一个组合框依赖于另一个组合框

Question

这是我的代码;

 comboBoxAdminVisit.DataSource = be.Events; 
     comboBoxAdminVisit.DisplayMember = "EventName"; 


     var fff = (from cc in be.Visitors 
        select cc.Attending).FirstOrDefault(); 

     var ggg = (from xx in be.Events 
        where xx.Id == fff 
        select xx.Id).FirstOrDefault(); 

     if (fff == ggg) 
     { 
      foreach (var name in comboBoxAdminName.Items) 
      { 
       comboBoxAdminName.Items.Add(name); 
      } 

cc.Attending是一个外键，它存储事件tabel的priomary键。我想从第一个组合框中选择一个事件，然后让第二个组件参与事件。提前致谢！

Events  Visitors 
------  -------- 
Id   Id 
Attendee(FK) Name 
EventName Company 
EventStart Car Reg 
EventEnd  Visiting 

Answer 1

我不知道你的实体的确切结构，但这里是一个想法如何实现它：

private void Form1_Load(object sender, EventArgs e) 
{ 
    comboBoxAdminVisit.DataSource = be.Events; 
    comboBoxAdminVisit.DisplayMember = "EventName"; 
} 

private void comboBoxAdminVisit_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    if (comboBoxAdminVisit.SelectedItem != null) 
    { 
     Event selectedEvent = (Event)comboBoxAdminVisit.SelectedItem; 

     var visitors = (from cc in be.Visitors 
         where cc.Attending.Events.Contains(x => x.EnventId = selectedEvent.Id) 
         select cc); 

     comboBoxAdminName.DataSource = visitors; 
     comboBoxAdminName.DisplayMember = "Name"; 
    } 
}