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null value

Posted on 2004-08-21
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Last Modified: 2010-05-02
I have a application in visual basic with access as backend
In the form if I take value for any text box and save it in the database
And next time while editing if I try to make it null and save it
Next time I get the error invalid use of null although I have checked for no values required
In the access and default value to “”

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Question by:leenapedenekar
6 Comments
 
LVL 76

Expert Comment

by:GrahamSkan
ID: 11858012
It sounds as if you are succcessfully reading a null value from the database and then trying to do something with it in VB that cannot be done with a Null.
You'll need to test for null before you use it.

If Not MyVariable Is Null Then
...
End If
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Colosseo earned 25 total points
ID: 11858043
Graham should that not be

If Not IsNull(MyVariable) Then
...
End If
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Expert Comment

by:Ryan Chong
ID: 11858062
also can try like below, if you want to retrieve values from your db to textbox:

text1.text = "" & Rs("myfield")

this will make you ease and no need to check whether the value return is null or not.
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Expert Comment

by:GrahamSkan
ID: 11860282
Yes, Colloseo, you are right. A senior moment. I'm afraid.
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Expert Comment

by:JR2003
ID: 11863545
leenapedenekar

ryancys solution is probably the neatest for any text field.
Anytime you receive some text from the database that could possibly be null, just add & "" on the end of the line.

e.g. Text1.Text = Rs("myfield").Value & ""  

For date and numeric fields that can possibly be null just use the IsNull function

If IsNull(Rs("myfield").Value) Then
...
Else
...
End IF

JR
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