Linq到Sql，由2屬性和子字符串組

Question

我有一個初始查詢，我想要修改，以增加我的結果中的粒度。但Visual Studio告訴我，我的查詢是無效的，我不明白爲什麼。基本上我想根據2個屬性（列）對數據進行分組，並按照前N個字符對其中一個屬性進行分組。

，工程初始查詢：

List<PostalCode> codes = (from customer in bd.Customers 
         group customer by customer.postalcode.Substring(0, postalCodeLength) into postalCodes 
         select new PostalCode 
         { 
          Postal = postalCodes.Key, 
          Count = postalCodes.Count() 
         }).ToList(); 
       return codes; 

查詢被標記爲**錯了VS2010：

List<PostalCode> codes = (from customer in bd.Customers 
          group customer by new { **customer.postalcode.Substring(0, postalCodeLength)**, customer.CustomerGroupType} 
          into postalCodes 
          select new PostalCode 
          { 
           Postal = postalCodes.Key.postalcode, 
           CustomerGroupType = postalCodes.Key.CustomerGroupType, 
           Count = postalCodes.Count() 
          }).ToList(); 
return codes; 

Answer 1

新{}對象語法要求性能有名字 - 這是你原來的查詢做不需要。它不能從您的方法調用中推斷出一個名稱。所以我建議將其改爲如下：

from customer in bd.Customers 
group customer by new { TrimmedPostalCode = customer.postalcode.Substring(0, postalCodeLength), customer.CustomerGroupType} 
into postalCodes 
select new PostalCode 
{ 
    Postal = postalCodes.Key.TrimmedPostalCode, 
    CustomerGroupType = postalCodes.Key.CustomerGroupType, 
    Count = postalCodes.Count() 
}