c# - 如何使用 linq 在选择查询中获取值？

Question

我使用 LINQ 内部联接合并了 2 个表 Clients 和 Payments。在此之后，我用这两个表中的值填充一个新模型 Totals。我只需要获取一个用户名。有任何想法吗？我将非常感激!

var results = from client in _db.Clients
                          join trade in _db.Payments on client.Id equals trade.ClientId
                          where (client.Id == trade.ClientId &&
                          DateTime.Compare(trade.TradeDate, (DateTime)fromDate) >= 0 &&
                          DateTime.Compare(trade.TradeDate, (DateTime) toDate) <= 0)
                          select new { client.Username, trade};
            var cs = results
                .GroupBy(tr => tr.trade.ClientId)
                .Select(item => new Totals
                {
                    Username = //here I need to set a value
                    CommBcf = item.Sum(client => client.trade.CommBcf),
                    EcnAll = item.Sum(client => client.trade.EcnAll),
                    EcnRbt = item.Sum(client => client.trade.EcnRbt),
                    OpenGross = item.Sum(client => client.trade.OpenGross),
                    CloseGross = item.Sum(client => client.trade.CloseGross)
}).ToList();

Answer 1

按键和名称分组。您可以通过使用 new {id,name} 创建新的匿名对象来按多列分组。

 var results = from client in _db.Clients
                              join trade in _db.Payments on client.Id equals trade.ClientId
                              where (client.Id == trade.ClientId &&
                              DateTime.Compare(trade.TradeDate, (DateTime)fromDate) >= 0 &&
                              DateTime.Compare(trade.TradeDate, (DateTime) toDate) <= 0)
                              select new { client.Username, trade};
                var cs = results
                    .GroupBy(tr => new {id=tr.trade.ClientId,name=tr.trade.Name})
                    .Select(item => new Totals
                    {
                        Username = item.Key.name
                        CommBcf = item.Sum(client => client.trade.CommBcf),
                        EcnAll = item.Sum(client => client.trade.EcnAll),
                        EcnRbt = item.Sum(client => client.trade.EcnRbt),
                        OpenGross = item.Sum(client => client.trade.OpenGross),
                        CloseGross = item.Sum(client => client.trade.CloseGross)
    }).ToList();