Linq Group By

Question

我有一个抽象类，其中收件人可以是EMailRecipient或SMSRecipients。

我在List List<Recipient>中选择数据。出于统计原因，我需要根据SMSRecipient中的CountryCode知道接收者的数量，我想我可以在linq中做到这一点。但我似乎无法将收件人转为像

这样的SMSRecipient

var q = from v in AMessageQueueContentList
        group v by (FlexyNet.Data.SMSRecipient)v.Recipient into g
        select count(g);

我的班级看起来像这样：

public abstract class Recipient
{
    public int MemberID { get;set;}
    public Recipient(){}
}

public class EMailRecipient : Recipient
{
    public string EMail { get; set; }
    public bool ValidMail { get; set; }

    public EMailRecipient(FlexyDataReader read)
    {
        this.MemberID = (int)read["MemberID"];
        this.EMail = (string)read["Recipient"];
    }

    public EMailRecipient(int memberID,string eMail)
    {
        this.MemberID = memberID;
        this.EMail = (string)eMail;
    }


}

public class SMSRecipient : Recipient
{
    public string Number { get; set; }
    public string CountryCode { get; set; }
    public nimta.Recipient NimtaRecipient { get; set; }
}

Answer 1

你可以这样做吗？

var counts = from m in AMessageQueueContentList
             let s = m.Recipient as FlexyNet.Data.SMSRecipient
             where s != null
             group s by s.CountryCode into g
             select new { CountryCode = g.Key, Count = g.Count() };

或者，如果您确实有一个Recipient对象列表，则可以使用LINQ的OfType<T>()扩展方法：

var sms = recipients.OfType<FlexyNet.Data.SMSRecipient>();
var counts = from s in sms
             group s by s.CountryCode into g
             select new { CountryCode = g.Key, Count = g.Count() };