IEnumerable的 <T> 使用匿名方法

Question

我不知道如何擺脫這個錯誤？

錯誤1使用通用類型'System.Collections.Generic.IEnumerable'需要1個類型參數C：\\ Users \\ huzaifa.gain \\ documents \\ visual studio 2010 \\ Projects \\ VendInvoiceImport \\ VendInvoiceImport \\ Program.cs 34 24 VendInvoiceImport

private static IEnumerable<string , string >  DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
       {
           var InvoiceLinecollection = VendorInvoiceStagingTable.AsEnumerable().Select(t => new {  number = t.Field<string>(VendInvoice.Number),LineNumber = t.Field<string>(VendInvoice.LineNumber)}).Distinct();
        return InvoiceLinecollection;
      }

Answer 1

您的Linq查詢返回一個匿名類型序列，但是方法不能返回匿名類型。 您有幾種選擇：

• 返回IEnumerable<Tuple<string, string>>

   private static IEnumerable<Tuple<string, string>> DistinctInvoiceNumber(DataTable VendorInvoiceStagingTable) { var InvoiceLinecollection = VendorInvoiceStagingTable .AsEnumerable() .Select(t => Tuple.Create(t.Field<string>(VendInvoice.Number), t.Field<string>(VendInvoice.LineNumber))) .Distinct(); return InvoiceLinecollection; } 

• 根據另一個答案的建議返回IDictionary<string, string> （假設查詢不返回重復的鍵）

   private static IDictionary<string, string> DistinctInvoiceNumber(DataTable VendorInvoiceStagingTable) { var InvoiceLinecollection = VendorInvoiceStagingTable .AsEnumerable() .Select(t => Tuple.Create(t.Field<string>(VendInvoice.Number), t.Field<string>(VendInvoice.LineNumber))) .Distinct() .ToDictionary(t => t.Item1, t => t.Item2); return InvoiceLinecollection; } 

• 為此創建一個具有2個字符串屬性的類，並返回該類的序列

   private static IEnumerable<InvoiceLine> DistinctInvoiceNumber(DataTable VendorInvoiceStagingTable) { var InvoiceLinecollection = VendorInvoiceStagingTable .AsEnumerable() .Select(t => new InvoiceLine(t.Field<string>(VendInvoice.Number), t.Field<string>(VendInvoice.LineNumber))) .Distinct(); return InvoiceLinecollection; } 

Answer 2

為什么不使用Dictionary<string, string>呢？

private static Dictionary<string , string >  DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
       {
           var InvoiceLinecollection = VendorInvoiceStagingTable.AsEnumerable().Select(t => new {  number = t.Field<string>(VendInvoice.Number),LineNumber = 
                 t.Field<string>(VendInvoice.LineNumber)}).ToDictionary();
            return InvoiceLinecollection;
          }