如何将多重联接中的所有字段包含在 Linq 语句中

本文关键字：字段 包含 语句 Linq | 更新日期: 2023-09-27 17:56:18

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
          };

在上面的联接语句中，"详细信息"是一个列表，但它仅包含"发票"和"跟踪"列。我也希望能够从发票行获取列。

提前谢谢。

如何将多重联接中的所有字段包含在 Linq 语句中

如果要获取发票的行信息列表，则需要将into移动到第一个join，然后在外部select内执行其他join。

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 }
    };

作为 Ivan 解决方案的替代方案，应该会产生更好的性能。

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)
  };
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