nullable object must have a value

Question

There is paradox in the exception description  Nullable object must have a value       This is the problem   I have a DateTimeExtended class   that has       DateTime  MyDataTime    int  otherdata       and a constructor  DateTimeExtended DateTimeExtended myNewDT       this MyDateTime   myNewDT MyDateTime Value     this otherdata   myNewDT otherdata      running this code  DateTimeExtended res   new DateTimeExtended oldDTE     throws an InvalidOperationException with the message      Nullable object must have a value    myNewDT MyDateTime Value - is valid and contain a regular DateTime object   What is the meaning of this message and what am I doing wrong   Note that oldDTE is not null  I ve removed the Value from myNewDT MyDateTime but the same exception is thrown due to a generated setter

User · Answer

Looks like oldDTE MyDateTime was null  so constructor tried to take it s Value - which threw

User · Answer

Assign the members directly without the  Value part   DateTimeExtended DateTimeExtended myNewDT       this MyDateTime   myNewDT MyDateTime     this otherdata   myNewDT otherdata

User · Answer

I got this message when trying to access values of a null valued object   sName   myObj Name    this will produce error  First you should check if object not null  if myObj    null    sName   myObj Name    This works

User · Answer

In this case oldDTE is null  so when you try to access oldDTE Value the InvalidOperationException is thrown since there is no value  In your example you can simply do   this MyDateTime   newDT MyDateTime

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When using LINQ extension methods  e g  Select  Where   the lambda function might be converted to SQL that might not behave identically to your C  code  For instance  C  s short-circuit evaluated  amp  amp  and    are converted to SQL s eager AND and OR  This can cause problems when you re checking for null in your lambda   Example   MyEnum  type   null  Entities Table Where a   gt  type    null         a type     int type  ToArray        Exception  Nullable object must have a value

User · Answer

You should change the line this MyDateTime   myNewDT MyDateTime Value  to just this MyDateTime   myNewDT MyDateTime   The exception you were receiving was thrown in the  Value property of the Nullable DateTime  as it is required to return a DateTime  since that s what the contract for  Value states   but it can t do so because there s no DateTime to return  so it throws an exception   In general  it is a bad idea to blindly call  Value on a nullable type  unless you have some prior knowledge that that variable MUST contain a value  i e  through a  HasValue check     EDIT  Here s the code for DateTimeExtended that does not throw an exception   class DateTimeExtended       public DateTime  MyDateTime      public int  otherdata       public DateTimeExtended            public DateTimeExtended DateTimeExtended other                this MyDateTime   other MyDateTime          this otherdata   other otherdata            I tested it like this   DateTimeExtended dt1   new DateTimeExtended    DateTimeExtended dt2   new DateTimeExtended dt1     Adding the  Value on other MyDateTime causes an exception  Removing it gets rid of the exception  I think you re looking in the wrong place

User · Answer

Try dropping the  value  DateTimeExtended DateTimeExtended myNewDT       this MyDateTime   myNewDT MyDateTime     this otherdata   myNewDT otherdata

User · Answer

I got this solution and it is working for me if  myNewDT MyDateTime    null       myNewDT MyDateTime   DateTime Now

[c#] nullable object must have a value

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