如何从州获得城市摘要

Question

我的SQL Server数据库中有一个State和一个Cities表（如下面的屏幕快照所示）。在我的C＃Winforms项目中，我试图通过使用LINQ查询来生成州和每个州的城市数，但是它不能按我的意愿工作。

这是我的代码：

var states = (from u in db.States
              join c in db.City on u.StateId equals c.StateId
              group u by u.City into g 
              select new 
              {
                  StateId=  u.StateId, 
                  State Name = u.StateName,  // Maybe g.Key here ??
                  Total Cities = g.Count     // and here I am not sure
              }).ToList();

 dgvStates.DataSource = states;

Answer 1

尝试这个：

var states = from u in db.States
             join c in db.City on u.StateId equals c.StateId
             group u by u.StateName into g 
             select new 
             {
                StateName = g.Key,
                TotalCities = g.Count()
             };

请参见示例https://dotnetfiddle.net/1bqhTM

上面代码的结果

Answer 2

这段代码可以工作：

public void LoadStates()
        {

            try
            {
                TESTEntities db = new TESTEntities();

                // cmbProvince.Text = "";

                var states = (from u in db.States


                                select new
                                {
                                    u.StateId,

                                    u.StateName,
                                    u.Cityies.Count
                                }).ToList();


                dgvStates.DataSource = states;
                dgvStates.Columns[0].Visible = false;

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }


        }