LINQ – 分组/汇总多列

数据是本地CSV文件，通过OleDB加载到ado.net数据集中。 该表有40多个列，包括发票详细信息。 每行是发票中的单独行项目，可以包含1到n行。

该查询用于将发票明细分组为每个发票的单行，总计发票金额和到期余额。

以下工作，我正在尝试确定：是否可以在单个查询中执行此操作？

//group the invoices by invoicenumber and sum the total //Zoho has a separate record (row) for each item in the invoice //first select the columns we need into an anon array var invoiceSum = DSZoho.Tables["Invoices"].AsEnumerable() .Select (x => new { InvNumber = x["invoice number"], InvTotal = x["item price"], Contact = x["customer name"], InvDate = x["invoice date"], DueDate = x["due date"], Balance = x["balance"], } ); //then group and sum var invoiceTotals = invoiceSum .GroupBy (s => new {s.InvNumber, s.Contact, s.InvDate, s.DueDate} ) .Select (g => new { InvNumber = g.Key.InvNumber, InvDate = g.Key.InvDate, DueDate = g.Key.DueDate, Contact = g.Key.Contact, InvTotal = g.Sum (x => Math.Round(Convert.ToDecimal(x.InvTotal), 2)), Balance = g.Sum (x => Math.Round(Convert.ToDecimal(x.Balance), 2)), } ); 

Answer 1

实际上，当您使用invoiceTotals的结果时，您只执行一个查询。 在您显示的代码中，您甚至没有对数据库进行查询。

谷歌“linq延期执行”，它很漂亮;-)

但正如Uriil所说，你可以将这些语句组合成一个linq查询：

 var invoiceSum = DSZoho.Tables["Invoices"].AsEnumerable() .Select (x => new { InvNumber = x["invoice number"], InvTotal = x["item price"], Contact = x["customer name"], InvDate = x["invoice date"], DueDate = x["due date"], Balance = x["balance"], } ) .GroupBy (s => new {s.InvNumber, s.Contact, s.InvDate, s.DueDate} ) .Select (g => new { InvNumber = g.Key.InvNumber, InvDate = g.Key.InvDate, DueDate = g.Key.DueDate, Contact = g.Key.Contact, InvTotal = g.Sum (x => Math.Round(Convert.ToDecimal(x.InvTotal), 2)), Balance = g.Sum (x => Math.Round(Convert.ToDecimal(x.Balance), 2)), } );