我怎么能隐式转换类型System.DateTime？到System.DateTime [英] How can I implicitly convert type System.DateTime? to System.DateTime

问题描述

public class StudentDetails
{
public string Type{get; set;}
public DateTime StartDate { get; set; }
public string Name { get; set; }
public string Status { get; set; }
public DateTime EndDate { get; set; }
public string Course { get; set; }
}

我使用上面的代码创建了List，并在以下代码中使用它：

I have created List using above code and is used it in a following code :

[WebMethod]
public StudentDetails[] GetTodayReport(int StudentID, DateTime startdate)
{
DateTime tartdate = DateTime.UtcNow.AddDays(-3);
try
{
context = new TMSEntities();
// List<studentdetails> details = new List<studentdetails>();

List<string> sdetails = new List<string>();
DataTable NewTable = new DataTable();
NewTable.Columns.AddRange(new DataColumn[6] { new DataColumn("Type", typeof(string)),   new DataColumn("StartDate", typeof(string)), new DataColumn("Name", typeof(string)), new DataColumn("Status", typeof(string)), new DataColumn("EndDate", typeof(string)), new DataColumn("Course", typeof(string)) });
var query = (from E in context.tbl_ExamCreation
             join EA in context.tbl_ExamAttendence on E.Exam_ID equals EA.Exam_ID
             join C in context.tbl_Course on E.Course_ID equals C.CourseID
             where EA.StudentID == StudentID && SqlFunctions.DateDiff("DAY", E.DateOfExam, tartdate) == 0 && E.Status == "A"
             select new { Type = "Exam", StartDate = E.DateOfExam, Name = E.ExamName, Status = EA.status, EndDate = E.ExamEndDatetime, Course = C.Name })
           .Union
           (from LS in context.tbl_LectureScheduling
            join LA in context.tbl_LectureAttendence on LS.LectureScheduleID equals LA.LectureScheduleID
            join L in context.tbl_Lectures on LS.LectureID equals L.LectureID
            join CR in context.tbl_Course on L.CourseID equals CR.CourseID
            where LA.StudentID == StudentID && SqlFunctions.DateDiff("DAY", LS.StartDateTime, startdate) == 0 && LS.Status == "A"
            select new { Type = "Lecture", StartDate = LS.StartDateTime, Name = L.LectureName, Status = LA.status, EndDate = LS.EndDateTime, Course = CR.Name }
            );
return query.Select(x=>new StudentDetails() { Type = x.Type, StartDate = x.StartDate, Name = x.Name, Status = x.Status , EndDate = x.EndDate, Course = x.Course }).ToArray();
}
catch (Exception ex)
{
return null;
}
}
}

但是X.StartDate和x.EndDate发生了错误：

错误23无法将类型'System.DateTime？'隐式转换为'System.DateTime'。存在显式转换（您是否错过了演员？）



如果存在解决方案，请告诉我

推荐答案

你可以使用这个例子：

You can use this example:

DateTime? nullableDate = new DateTime();
DateTime regularDate = nullableDate.HasValue ? nullableDate.Value : default(DateTime);

你的班级：

your class:

public class StudentDetails
{
public string Type{get; set;}
public DateTime StartDate { get; set; }
public string Name { get; set; }
public string Status { get; set; }
public DateTime EndDate { get; set; }
public string Course { get; set; }
}

更改如下：

Change like below:

public class StudentDetails
{
public string Type{get; set;}
public DateTime? StartDate { get; set; }
public string Name { get; set; }
public string Status { get; set; }
public DateTime? EndDate { get; set; }
public string Course { get; set; }
}

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