Linq到Sql，由2属性和子字符串组

Question

我有一个初始查询，我想要修改，以增加我的结果中的粒度。但Visual Studio告诉我，我的查询是无效的，我不明白为什么。基本上我想根据2个属性（列）对数据进行分组，并按照前N个字符对其中一个属性进行分组。

，工程初始查询：

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; 

查询被标记为**错了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{}对象语法要求性能有名字 - 这是你原来的查询做不需要。它不能从您的方法调用中推断出一个名称。所以我建议将其改为如下：

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() 
}