Null in datetime

DARSIN · January 25th, 2005, 08:13 AM

Can i aSSIGN NULL to a DateTime

Imar · January 25th, 2005, 01:35 PM

I don't think so. However, you can assign it DateTime.MinValue and then consider anything that equals DateTime.MinValue to be null.

Cheers,

Imar
---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.

Vadivel · January 25th, 2005, 02:42 PM

Normally we would try to use DBNull.Value .. instead try SqlDateTime.Null .. it would work.

1. Make use of namespace :: System.Data.SqlTypes
2. SqlDateTime strSql; //Declare a variable
3. strSql = SqlDateTime.Null; //assigning null to that variable

Use this variable while adding parameters to the command object.

Best Regards
Vadivel

MVP ASP/ASP.NET
http://vadivel.thinkingms.com

mehdi62b · January 25th, 2005, 03:14 PM

null is a reference type while DateTime is a value type(struct) so you can't assign them together.

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mehdi62b · January 26th, 2005, 11:39 AM

Ops!I should edit my previous post,
we can assign an object to a struct like DateTime(Unboxing) and also a struct to an object(Boxing),

Code:

DateTime dt1=new DateTime(m,y,d);
object o=dt1//Boxing
DateTime dt2=(DateTime)o//Unboxing

but about null,as I think there is nothing in null!so we can't use Boxing and Unboxing.

_____________________________
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software engineering student.
Looking for a good job for summer 2005.

Vadivel · January 26th, 2005, 01:17 PM

Check this out :: http://www.c-sharpcorner.com/Code/20...orDateTime.asp

Best Regards
Vadivel

MVP ASP/ASP.NET
http://vadivel.thinkingms.com

Imar · January 26th, 2005, 01:56 PM

The article deals with inserting null in the database, for which DBNull.Value is indeed the most logical option.

However, the OP asked if you can assign null to a DateTime value.

Consider a simple class like this:

Code:

    public class Person
    {
    private DateTime birthDay;

    public void Save()
    {
        // save person to database
    }

    public DateTime BirthDay
    {
      get
      {
        return birthDay;
      }
      set
      {
        birthDay = value;
      }
    }
    }

How would you, inside the Save method, determine what the value of birthDay is? The article you linked to compares txtDate.Text against "" which just checks for an empty string.
However, inside your class, there is no textbox (or calendar control or whatever) to compare with. All you have is the backing birthDay variable.

There must be other ways to do this, but I usually use DateTime.MinValue to initialize the birthDay variable.
Then in the Save method, I check if the birthDay is still MinValue. If it is, I consider it to be equal to DBNull.Value and update my database accordingly.

Cheers,

Imar

mehdi62b · January 26th, 2005, 06:15 PM

Imar,I think like DateTime you obey the same logic for int or float or decimal,but I have a question here,what can we do for bool type?

_____________________________
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software engineering student.
Looking for a good job for summer 2005.

Imar · January 26th, 2005, 06:19 PM

What do you mean with "obey the same logic for int or float or decimal"?

For bool you don't have much options, I guess. You can either initialize them to true or false. What you choose probably depends on what default value makes the most sense in your specific application.

The same applies to the other types you mentioned; you'll have to provide a sensible default....

Cheers,

Imar
---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.
While typing this post, I was listening to: Made For TV Movie by Incubus (Track 11 from the album: A Crow Left Of The Murder...) What's This?

mehdi62b · January 27th, 2005, 08:53 AM

sorry,I wasn't clear enough,
suppose for a person I have a boolean field in DB,it could have tree values,

1-True
2-False
3-null

and in my C# code I would have something like below,

Code:

public class Person
{
    private DateTime birthDay;
    private bool isSingle;
    //...
    public bool IsSingle
    {
      get
      {
        return isSingle;
      }
      set
      {
        isSingle = value;
      }
    }
    //...
}

now for DateTime if in DB it has a null value,in C# code I choose DateTime.MinValue...(like other types for example if an integer field in DB has a null value I represent it with int.MinValue),but for bool there is nothing except true or false...
I found two solutions,

1-new structure (it uses operator overloading so in VB.NET...)
2-SqlBoolean

Thanks.:)

_____________________________
Mehdi.
software engineering student.
Looking for a good job for summer 2005.