IEnumerable <T>用匿名方法

Question

我不知道如何摆脱这个错误？

错误1使用泛型类型'System.Collections.Generic.IEnumerable'需要1个类型参数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查询返回一个匿名类型的序列，但方法不能返回匿名类型。您有几种选择：

• 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; 
  } 
  

• 回报作为另一个答案建议（假设你的查询不返回重复键）

  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; 
  } 
  

• 一个IDictionary<string, string>用2个字符串属性为此创建一个类并返回该类的序列

  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

为什么你不使用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; 
      }