How to compare a DBnull expression

Question

I have the following code:

dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt")

Which has value of DBnull.

now I want to compare it:

if dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt")=nothing

....

...

I get

Run-time exception thrown : System.InvalidCastException - Operator is not valid for type 'DBNull' and 'Nothing'.

Ideas how to compare this value to see if it contains a DBnull?

if dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt")=system.DBnull also returns an error.

Refer: http://stackoverflow.com/questions/222834/handling-dbnull-data-in-vb-net — A Coder, Sep 10 '13 at 19:23

score 4 · Answer 1 · answered Sep 10 '13 at 19:21

4

You can either use the IsDBNull() function

If IsDbNull(dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt")) Then ...

or compare agains DBNull.Value

If dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt") Is DBNull.Value Then ...

answered Sep 10 '13 at 19:21

Dennis Traub

score 2 · Answer 2 · answered Sep 10 '13 at 21:02

2

Another option is to use Convert.DBNull (same as DBNull.Value):

If dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt") Is Convert.DBNull Then
  ' value is null
End If

I prefer this syntax, because it's very similar to Is Nothing comparison.

answered Sep 10 '13 at 21:02

Victor Zakharov

score 1 · Accepted Answer · answered Sep 10 '13 at 19:21

1

Use IsDBNull function:

Returns a Boolean value that indicates whether an expression evaluates to the System.DBNull class.

If IsDBNull(dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt")) Then
    ' value is null
End If

answered Sep 10 '13 at 19:21

MarcinJuraszek

Checking ... As this reply came first., – S Nash Sep 10 '13 at 19:30
@SNash Actually, it was not the first one. – MarcinJuraszek Sep 10 '13 at 19:35
I saw your reply came 30 seconds before Dennis Traub – S Nash Sep 12 '13 at 12:02

score 1 · Answer 4 · answered Sep 10 '13 at 19:22

1

DBNull.Value provides a way to do comparisons. So you can write:

if dsParticippantInfo.Tables(0).Rows(0)("Contract_Amt")=DBNull.Value

answered Sep 10 '13 at 19:22

Boluc Papuccuoglu

Well, C# is my "native language" so I'm not 100%, but using this link: http://msdn.microsoft.com/en-us/library/system.dbnull.value.aspx?cs-save-lang=1&cs-lang=vb#code-snippet-1 , I thought that `DBNull.Value.Equals(a)` was the equivalent of `a=DBNull.Value` (That would be `DBNull.Value==a` in C#) Was I wrong? – Boluc Papuccuoglu Sep 10 '13 at 19:26

score 0 · Answer 5 · answered Sep 10 '13 at 19:23

0

Try this:

`If IsDbNull() Then
 End If
`

answered Sep 10 '13 at 19:23

A Coder

5 Answers5