There must be a value for a nullable object.

Problem

The exception description contains a paradox: a nullable object must have a value (?!)

The difficulty is this:

I have a DateTimeExtended class that has the following properties:

{
  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);

with the message: raises an InvalidOperationException

myNewDT.MyDateTime.Value – contains a standard DateTime object and is valid.

What does this message indicate, and what am I doing wrong?

It’s worth noting that oldDTE isn’t null. Value has been withdrawn from myNewDT. MyDateTime, however owing to a generated setter, the same issue is thrown.

Asked by Dani

Solution #1

This line should be changed. myNewDT = myDateTime MyDateTime. To simply this, there is value. myNewDT = myDateTime MyDateTime;

The exception you were getting was tossed into the mix. The Nullable DateTime’s Value property is expected to return a DateTime (as stated in the contract for.Value), but it can’t because there isn’t one to return, therefore it throws an exception.

In general, calling on a whim is a bad idea. Unless you have some prior knowledge that the variable MUST contain a value, don’t use a value on a nullable type (i.e. through a .HasValue check).

EDIT

The code for DateTimeExtended that doesn’t throw an exception is as follows:

class DateTimeExtended
{
    public DateTime? MyDateTime;
    public int? otherdata;

    public DateTimeExtended() { }

    public DateTimeExtended(DateTimeExtended other)
    {
        this.MyDateTime = other.MyDateTime;
        this.otherdata = other.otherdata;
    }
}

This is how I put it to the test:

DateTimeExtended dt1 = new DateTimeExtended();
DateTimeExtended dt2 = new DateTimeExtended(dt1);

Adding the to the equation. Other people’s worth. An exception is thrown by MyDateTime. The exception is removed when it is removed. You’re looking in the incorrect spot, I believe.

Answered by Yuliy

Solution #2

The lambda function may be translated to SQL when utilizing LINQ extension methods (e.g. Select, Where), which may not behave exactly like your C# code. Short-circuit evaluated && and || in C#, for example, are transformed to eager AND and OR in SQL. When checking for null in your lambda, this can cause issues.

Example:

MyEnum? type = null;
Entities.Table.Where(a => type == null || 
    a.type == (int)type).ToArray();  // Exception: Nullable object must have a value

Answered by Protector one

Solution #3

Remove the.value from the equation.

DateTimeExtended(DateTimeExtended myNewDT)
{
   this.MyDateTime = myNewDT.MyDateTime;
   this.otherdata = myNewDT.otherdata;
}

Answered by Paul Creasey

Solution #4

Without the.Value component, assign the members directly:

DateTimeExtended(DateTimeExtended myNewDT)
{
   this.MyDateTime = myNewDT.MyDateTime;
   this.otherdata = myNewDT.otherdata;
}

Answered by Cecil Has a Name

Solution #5

Because oldDTE is null in this example, an InvalidOperationException is issued when you try to access oldDTE.Value because there is no value. You can just do the following in your case:

this.MyDateTime = newDT.MyDateTime;

Answered by Lee

Post is based on https://stackoverflow.com/questions/1896185/nullable-object-must-have-a-value