Linq to Sql，按2属性和子字符串分组

本文关键字：字符串 属性 to Sql Linq | 更新日期: 2023-09-27 18:17:00

我有一个初始查询，我想修改它以增加结果的粒度。但是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属性(列)分组我的数据，并通过前N个字符分组属性之一。

有效的初始查询:

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;

用**标记的查询是错误的:

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;

Linq to Sql，按2属性和子字符串分组

新的{}对象语法要求属性有名称——这是您最初的查询所不需要的。它不能从方法调用中推断出名称。所以我建议把它改成:

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() 
}
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