如何在Linq语句的多重联接中包含所有字段？

Question

var largeset =
from invs in context.Invoices
join lines in context.InvoiceLines on invs.InvoiceId equals lines.InvoiceId
join tracks in context.Tracks on lines.TrackId equals tracks.TrackId into grp
select new
          {
              Invoice = invs,
              Detail = grp
          };

在上面的join into语句中，Detail是一个列表，但仅包含Invoice和Track列。 我也希望能够从InvoiceLine获取列。

提前致谢。

Answer 1

如果你想获得的行信息列表发票，你需要移动into的第一join并执行其他join内外部select 。

像这样：

var largeset =
    from inv in context.Invoices
    join line in context.InvoiceLines on inv.InvoiceId equals line.InvoiceId into lines
    select new
    {
        Invoice = inv,
        Lines =
            from line in lines
            join track in context.Tracks on line.TrackId equals track.TrackId
            select new { Line = line, Track = track }
    };

Answer 2

作为Ivan解决方案的替代方案，它应产生更好的性能。

var largeset =
  from invs in context.Invoices
  join lines in context.InvoiceLines on invs.InvoiceId equals lines.InvoiceId
  join tracks in context.Tracks on lines.TrackId equals tracks.TrackId
  group new { invs, lines, tracks }
  by new
  {
      invs.InvoiceId,
      invs.InvoiceDate,
      invs.CustomerId,
      invs.Customer.LastName,
      invs.Customer.FirstName
  } into grp
  select new
  {
      InvoiceId = grp.Key.InvoiceId,
      InvoiceDate = grp.Key.InvoiceDate,
      CustomerId = grp.Key.CustomerId,
      CustomerLastName = grp.Key.LastName,
      CustomerFirstName = grp.Key.FirstName,
      CustomerFullName = grp.Key.LastName + ", " + grp.Key.FirstName,
      TotalQty = grp.Sum(l => l.lines.Quantity),
      TotalPrice = grp.Sum(l => l.lines.UnitPrice),
      Tracks = grp.Select(t => t.tracks)
  };