Solved

Question on output parameter in VB.NET program.

Posted on 2006-07-20
3
197 Views
Last Modified: 2008-02-26
I have a stored proc:
CREATE proc usp_Test1    
@wo_num varchar(6),    
@emp_cd varchar(6) out,    
@status_message varchar(20) out    
as    
set @status_message = 'Print something'    
select @status_message, @emp_cd  
return    

When I run this stored proc: exec usp_Test1    '100000', 'aaa', 'bbb'
It has no error and will print: 'Print something'   'aaa'

But when I used in my vb.net program:
emp_cd = objCmd.Parameters("@emp_cd").Value
it will have an exception that shows:
"Cast from type 'DBNull' to type 'String' is not valid."

It's obviously because that output parameter was not assisgned a value.
1. But my question is, why it was null instead of getting the value from the parameter list in exec usp_Test1    '100000', 'aaa', 'bbb', i.e. got a value of 'aaa'?
2. My solution to the above problem was added one more initilization line:
set @emp_cd = ''  
Is there any better way or standard way of doing this? Thanks a lot.
0
Comment
Question by:heyday2004
  • 2
3 Comments
 
LVL 24

Expert Comment

by:Justin_W
ID: 17150761
I assume you have declared emp_cd as a String. If there is any possiblility that it can return NULL, you need to declare it as type Object, and only cast it to string if (DBNull.Value.Equals(emp_cd)) is false.
0
 
LVL 24

Assisted Solution

by:Justin_W
Justin_W earned 100 total points
ID: 17150764
FYI: This is because DBNull and Nothing/null are not the same thing in .NET.
0
 
LVL 24

Accepted Solution

by:
Jeff Certain earned 400 total points
ID: 17151541
For some reason, Microsoft has created an object called System.DBNull which represents an empty field. What's really baffling is that they made this object not cast to anything else (i.e. not string, integer, double)

The easiest way to deal with this is to rewrite your stored procedure to return something other than a NULL:
select @status_message, ISNULL(@emp_cd  ,'')
0

Featured Post

Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Introduction When many people think of the WebBrowser (http://msdn.microsoft.com/en-us/library/2te2y1x6%28v=VS.85%29.aspx) control, they immediately think of a control which allows the viewing and navigation of web pages. While this is true, it's a…
The ECB site provides FX rates for major currencies since its inception in 1999 in the form of an XML feed. The files have the following format (reducted for brevity) (CODE) There are three files available HERE (http://www.ecb.europa.eu/stats/exch…
Nobody understands Phishing better than an anti-spam company. That’s why we are providing Phishing Awareness Training to our customers. According to a report by Verizon, only 3% of targeted users report malicious emails to management. With compan…
The Email Laundry PDF encryption service allows companies to send confidential encrypted  emails to anybody. The PDF document can also contain attachments that are embedded in the encrypted PDF. The password is randomly generated by The Email Laundr…

770 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question