Testing for null value gives unexpected error

[Problematic coder]

Here is the code:

64 If objdr.Item("BD" ) = "" Or objdr.Item("BD" ) Is DBNull.Value Then
'test to see if result is blank or null
65 strBD = "00000000" 'No birthdate found so set to 8 spaces
66 Else
67 strBD = objdr.Item("BD" ) 'All ok so leave as is
68 End If

Here is the error I get:

System.InvalidC astException: Operator '=' is not defined for type
'DBNull' and string "".
at
Microsoft.Visua lBasic.Compiler Services.Operat ors.CompareObje ctEqual(Object
Left, Object Right, Boolean TextCompare)
at my_project.Form 1.Button1_Click (Object sender, EventArgs e) in C:
\...\Form1.vb:l ine 64

I am sure I have used this before with no problems, so am a little
confused...

Any thoughts?

Thanks for your time.

[Jack Jackson]

On Fri, 28 Sep 2007 17:19:56 -0000, Problematic coder
<gn******@gmail .comwrote:

>Here is the code:

64 If objdr.Item("BD" ) = "" Or objdr.Item("BD" ) Is DBNull.Value Then
'test to see if result is blank or null
65 strBD = "00000000" 'No birthdate found so set to 8 spaces
66 Else
67 strBD = objdr.Item("BD" ) 'All ok so leave as is
68 End If

Here is the error I get:

System.Invalid CastException: Operator '=' is not defined for type
'DBNull' and string "".
at
Microsoft.Visu alBasic.Compile rServices.Opera tors.CompareObj ectEqual(Object
Left, Object Right, Boolean TextCompare)
at my_project.Form 1.Button1_Click (Object sender, EventArgs e) in C:
\...\Form1.vb: line 64

I am sure I have used this before with no problems, so am a little
confused...

Any thoughts?

Thanks for your time.

The exception tells you what is wrong. You are trying to compare a
DBNull to a string.

Try changing the If to:
If objdr.Item("BD" ) Is DBNull.Value OrElse objdr.Item("BD" ) = ""
Then

This tests for DBNull.Value first and changing Or to OrElse prevents
the execution of the second test if the first is True.

[Problematic coder]

On Sep 28, 11:06 am, Jack Jackson <jacknos...@peb bleridge.comwro te:

On Fri, 28 Sep 2007 17:19:56 -0000, Problematic coder

<gnews...@gmail .comwrote:

Here is the code:

64 If objdr.Item("BD" ) = "" Or objdr.Item("BD" ) Is DBNull.Value Then
'test to see if result is blank or null
65 strBD = "00000000" 'No birthdate found so set to 8 spaces
66 Else
67 strBD = objdr.Item("BD" ) 'All ok so leave as is
68 End If

Here is the error I get:

System.InvalidC astException: Operator '=' is not defined for type
'DBNull' and string "".
at
Microsoft.Visua lBasic.Compiler Services.Operat ors.CompareObje ctEqual(Object
Left, Object Right, Boolean TextCompare)
at my_project.Form 1.Button1_Click (Object sender, EventArgs e) in C:
\...\Form1.vb:l ine 64

I am sure I have used this before with no problems, so am a little
confused...

Any thoughts?

Thanks for your time.

The exception tells you what is wrong. You are trying to compare a
DBNull to a string.

Try changing the If to:
If objdr.Item("BD" ) Is DBNull.Value OrElse objdr.Item("BD" ) = ""
Then

This tests for DBNull.Value first and changing Or to OrElse prevents
the execution of the second test if the first is True.- Hide quoted text -

- Show quoted text -

Makes total sense, thank you for the clear explanation