LINQ GroupBy 一个名称，但如何获取用户 ID？

Question

我想显示每个客户进行了多少次转账。
我想显示CustomerId、Name 和Totaly 的转账金额。
我的意思是我也想显示CustomerId，而不仅仅是Name 和Amount 转移。

除CustomerId 外，一切正常：在我的 DataGridview 中它是空的。
我不知道该怎么做，如果能提供任何帮助，我将不胜感激。

这是我的代码：

using (Db db = new Db())
{
   var statistic = (from u in db.Transfers
                    join c in db.Customers on u.CustomerId equals c.CustomerId
                    where u.IsActive == true && u.Paid == true
                    group u by c.FirstName  into g
                    select new
                    {
                      // here I get Headertext but not Id's value
                      Id = g.Select(x =>x.CustomerId),
                      Name = g.Key,
                      Totaly = g.Sum(x => x.Amount)
                    }).OrderByDescending(x => x.Totaly).ToList();
                    
                    if (statistic != null)
                    {
                        dgvCustomerList.DataSource = statistic;
                    }

}

Answer 1

正确的方法是按CustomerId 对其进行分组（因为CustomerId 是唯一的，您将在select 中获得不同的客户，然后您可以使用FirstOrDefault() 来获取FirstName 属性）：

    using (Db db = new Db())
{
   var statistic = (from u in db.Transfers
                    join c in db.Customers on u.CustomerId equals c.CustomerId
                    where u.IsActive == true && u.Paid == true
                    group u by c.CustomerId  into g
                    select new
                    {
                      Id = g.Key, // here I get Headertext but not Id's value
                      Name = g.FirstOrDefault().FirstName,
                      Totaly = g.Sum(x => x.Amount)
                    }).OrderByDescending(x => x.Totaly).ToList();
                    
                    if (statistic != null)
                    {
                        dgvCustomerList.DataSource = statistic;
                    }

}

Answer 2

您可以同时按customerId 和FirstName 进行分组

using (Db db = new Db())
{
   var statistic = (from u in db.Transfers
                    join c in db.Customers on u.CustomerId equals c.CustomerId
                    where u.IsActive == true && u.Paid == true
                    group u by new {key c.FirstName,key c.CustumerId}  into g
                    select new
                    {
                      Id = g.Key.CustumerId,//g.Select(x =>x.CustomerId), // here I get Headertext but not Id's value
                      Name = g.Key.FirstName,
                      Totaly = g.Sum(x => x.Amount)
                    }).OrderByDescending(x => x.Totaly).ToList();
                    
                    if (statistic != null)
                    {
                        dgvCustomerList.DataSource = statistic;
                    }

}