Question

如果userid为零，我该如何避免If条件到这种情况？

if (Userid == 0)
{
    var logList = service.GetLogDetails();
    var usernames = (from A in logList orderby A.FirstName select new { Name = A.FirstName + " " + A.SurName, ID = A.Id }).Distinct();
    var loginDate = (from A in logList select A.LogInTime.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)).Distinct();
    var logOutDate = (from A in logList select (A.LogOutTime ?? "Unknown").ToString().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)).Distinct();
}
else
{
    var logList = service.GetLogDetails();
    var usernames = (from A in logList where A.Id == Userid orderby A.FirstName select new { Name = A.FirstName + " " + A.SurName, ID = A.Id }).Distinct();
    var loginDate = (from A in logList where A.Id == Userid select A.LogInTime.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)).Distinct();
    var logOutDate = (from A in logList where A.Id == Userid select (A.LogOutTime ?? "Unknown").ToString().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)).Distinct();
}

Answer 1

在linq ||子句中使用where。您还可以通过查询logList一次，然后在其上应用不同的投影来改进：

var logList = service.GetLogDetails()
                     .Where(item => Userid == 0 || item.Id = Userid)
                     .ToList();

var usernames = (from A in logList 
                 orderby A.FirstName 
                 select new { Name = $"{A.FirstName} {A.SurName}", ID = A.Id }).Distinct();

var loginDate = (from A in logList 
                 select A.LogInTime.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)).Distinct();

var logOutDate = (from A in logList 
                  select (A.LogOutTime ?? "Unknown").ToString().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)).Distinct();

Answer 2

像这样修改您的查询

var usernames = (from A in logList where A.Id = UserId || UserId == 0 ...

C＃ - 如果Linq中的条件选择带有where子句的查询

2 个答案: