Error: Conversion from type DBNull to type string is not valid

Question

again i came for a problem. Please help me to do this. I was tried to get quantity from db make use of the selection in list box. I got answered with listbox1. If i selected the item in listbox1 the quantity would appear in textbox1. But in this same code will not work for listbox2 with textbox4.. Here i given the code...

 $Con.open()
 $Dim cd as new oledb.oledbcommand("Select Quantity from tlist where tool_name"& "'"listbox2.selecteditem & "'" & "", con)
 $dim rs as oledb.oledbdatareader
 $do while rs.read
 $textbox4.text=(rs("Quantity))
 $loop
 $con.close

Here i got the error as "Conversion from type DBNull to type string is not valid" Plz let me know what will i do.??

Alec Sanger · Accepted Answer · 2011-07-29 13:28:59Z

2

There are a few issues.

Your query is a bit off. It currently reads Select Quantity from tlist where tool_name'valueOfListbox2'". It should probably read Select Quantity from tlist where tool_name = 'valueOfListbox2'.
Your getting a null value back and are not checking for a null return before writing the value out, hence the error. You can use the following IF statement to verify your value is not null:

If NOT IsDbNull(rs("Quantity")) Then
Also, you're missing a double quote around "Quantity".

edited Jul 29, 2011 at 13:28

answered Jul 29, 2011 at 13:21

Alec Sanger

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