如何选择与分组的LINQ查询连接的字段

Question

我已经搜索了网站，并切片和切丁这几种不同的方式，但我是新来的LINQ，我无法弄清楚如何从我的连接表中选择字段。每次运行时，我都会收到一条消息：

“列UPC不属于表”。

“列条目不属于表”。

审计表对每个文件名都有一行数据，scanDetail表有多行与每个文件名关联。我需要加入这些表格，对数据进行分组，然后选择不同数量的UPC并仅显示最大条目号，以便每个文件名都有一行数据。

var query = from audit in audits.AsEnumerable()     
      join scan in scanDetail.AsEnumerable() 
      on audit.Field<string>("filename") equals scan.Field<string>("filename") 
      group audit by audit.Field<string>("filename") into g 
      select new 
      { 
       Account = g.Select(x => x.Field<string>("Account")), 
       Store = g.Select(x => x.Field<string>("Store")), 
       AuditDate = g.Select(x => x.Field<string>("AuditDate")), 
       UPCs = g.Select(x => x.Field<string>("UPC").Distinct().Count()), 
       Qty = g.Select(x => x.Field<string>("ScanQty")), 
       Retail = g.Select(x => x.Field<string>("RegTotal")), 
       Entries = g.Select(x => x.Field<string>("Entry").Max()), 
       Supervisor = g.Select(x => x.Field<string>("AuditSup")), 
       Division = g.Select(x => x.Field<string>("StoreDivision")), 
       Invoice = g.Select(x => x.Field<string>("InvAmount")) 
      }; 

我试过这种方式，结果相同。

var query = 
      from audit in audits.AsEnumerable() 

      join scan in scanDetail.AsEnumerable() 
      on audit.Field<string>("filename") equals 
      scan.Field<string>("filename") 
      group audit by new {storeDisk = audit.Field<string>("filename"), 
           Account = audit.Field<string>("Account"), 
           Store = audit.Field<string>("Store"), 
           AuditDate = audit.Field<string>("AuditDate"), 
           UPCs = (from UPC in scanDetail.AsEnumerable() 
             select scan.Field<string>("UPC")), 
           Qty = audit.Field<string>("ScanQty"), 
           Retail = audit.Field<string>("RegTotal"), 
           Entries = (from Entry in scanDetail.AsEnumerable() 
             select scan.Field<string>("Entry")), 
           Supervisor = audit.Field<string>("AuditSup"), 
           Division = audit.Field<string>("StoreDivision"), 
           Invoice = audit.Field<string>("InvAmount") 
      } into g 
      select new 
      { 

       Account = g.Key.Account, 
       Store = g.Key.Store, 
       AuditDate = g.Key.AuditDate, 
       UPCs = g.Select(x => x.Field<string>("UPC").Distinct().Count()), 
       Qty = g.Key.Qty, 
       Retail = g.Key.Retail, 
       Entries = g.Select(x => x.Field<string>("Entry").Max()), 
       Supervisor = g.Key.Supervisor, 
       Division = g.Key.Division, 
       Invoice = g.Key.Invoice 

      }; 

Answer 1

由于“的审计表具有用于每个文件名中的一行数据”，没有必要组从该表中的数据。在这种情况下，而不是常规的加入，你可以有根据documentation使用group join，：

进行关联两个序列的基础上平等的关键要素，并对结果进行分组。

换言之，对于外部表的每个元素你得到一个设置从内表相关元件的。然后您可以在该组上执行不同的聚合。请记住，在这种情况下，该集合可以是空的，并且一些聚合体会引发异常。

有了这样说，查询可能是这样的：

var query = from audit in audits.AsEnumerable()     
      join scan in scanDetail.AsEnumerable() 
      on audit.Field<string>("filename") equals scan.Field<string>("filename") 
      into scanGroup 
      select new 
      { 
       Account = audit.Field<string>("Account"), 
       Store = audit.Field<string>("Store"), 
       AuditDate = audit.Field<string>("AuditDate"), 
       UPCs = scanGroup.Select(scan => scan.Field<string>("UPC")).Distinct().Count(), 
       Qty = audit.Field<string>("ScanQty"), 
       Retail = audit.Field<string>("RegTotal"), 
       Entries = scanGroup.Select(scan => scan.Field<string>("Entry")).OrderByDescending(x => x).FirstOrDefault(), 
       Supervisor = audit.Field<string>("AuditSup"), 
       Division = audit.Field<string>("StoreDivision"), 
       Invoice = audit.Field<string>("InvAmount") 
      }; 

Answer 2

你基本上需要从要audit采取一切，把它放入该组的“关键”。

var query = from audit in audits.AsEnumerable()     
      join scan in scanDetail.AsEnumerable() 
      on audit.filename equals scan.filename 
      group audit by new { audit.Account, audit.Store, etc... } into g 
      select new 
      { 
       g.Key.Account, 
       g.Key.Store, 
       // etc for the rest of the audit fields 
       Entries = g.Max(x => x.Entry), 
       UPCs = g.Select(x => x.UPC).Distinct().Count()), 
      };