More In-Depth About Nulls And DBNull: ASP Alliance

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More In-Depth About Nulls And DBNull

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by Brian Mains
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ADO.NET

When working with ADO.NET, without a table adapter, to set a row's value to null, use the DBNull.Value construct. This can also work with command objects, when setting up the parameter. If you want to set a parameter to null, simply assign DBNull.Value to the command's parameter definition, as shown below:

Listing 7

Comand.Parameters.Add("@Field", SqlDbType.Varchar).Value = DBNull.Value

This translates to a null value in the database.

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Title: Nasty syntax for getting round this
Name: Tyrannosaurs
Date: 2/20/2008 11:50:11 AM
Comment:
You cast a null date time to a dbnull like this:

datetime? myDateTime;

myDateTime = null;

.... parameters.add(...).value = (object)myDateTime ?? System.DBNull.Value;

It's pretty horrible but works and is no worse than most of the alternatives.

Title: DBNULL
Name: g
Date: 11/19/2007 6:37:19 AM
Comment:
this concept can be dealt in more detail

Title: Datetime & DBNull Reply
Name: Brian
Date: 11/10/2007 11:29:55 PM
Comment:
You can't cast directly; DBNULL and DateTIme are two separate object types, and you can't cast one to the other. However, in an ADO.NET datarow object, the underlying value is object, which could accept both. However, if the field is not null, then you can't assign a null value to it. It all depends on your code.

Title: Datetime&DBnull
Name: Erick
Date: 11/9/2007 6:49:21 AM
Comment:
When I assigned DBNull.Value to System.Datetime, it raised a exception. Can I set a Datetime field of the database to null by using DBNull.Value in ADO.net?

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