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static void Main(string[] args)
{
//测试数据
List<UserMsg> ml = new List<UserMsg>() {
new UserMsg(){username="1",createtime=DateTime.Now.AddDays(-1).Date},
new UserMsg(){username="1",createtime=DateTime.Now.Date},
new UserMsg(){username="1",createtime=DateTime.Now.Date},
new UserMsg(){username="2",createtime=DateTime.Now.AddDays(-1).Date},
new UserMsg(){username="2",createtime=DateTime.Now.Date},
new UserMsg(){username="2",createtime=DateTime.Now.Date},
new UserMsg(){username="3",createtime=DateTime.Now.Date},
new UserMsg(){username="4",createtime=DateTime.Now.AddDays(-1).Date},
};
var q = from m in ml
where m.createtime == DateTime.Now.Date
group m by m.username into g1
select new
{
name = g1.Key,
isFirst=ml.Count(x=>x.username==g1.Key)>1?false:true,
};
foreach (var item in q)
{
Console.WriteLine(item.name+"---"+item.isFirst);
}
Console.ReadLine();
}
public class UserMsg
{
public string username { get; set; }
public DateTime createtime { get; set; }
}