Generating sensible Error Messages Using err.raise

Error Okay, I ' ll admit it, if there ' one area where my ASP scripts are Lacking:it's in the area of error checking. I ' ve looked at the Err object included with VBScript but have been really frustrated with it ' s seemingly lack On. (For more information on the ERR object is sure to read:error handling in asp!) Consider this snippet of code:

<%
Option Explicit

Dim Conn
Dim strSQL

Set Conn = Server.CreateObject ("ADODB. Connection ")
' This DSN does not exist
Conn.Open "Foo"
'...




If you run the above script (without has a DSN named Foo created) you'll get the following error:


Microsoft OLE DB Provider for ODBC Drivers error ' 80004005 '
[Microsoft] [ODBC Driver Manager] Data source name not found and no default driver specified

/dmsms/etest.asp, line 6

Fine, I can deal with that. While the error message is anything but pretty or profoundly descriptive, I do know that I need to fix something that ' s WR Ong on line 6 of the script. So I ' ll-load it into the editor, fix it and then try running it again. If needed I ' ll repeat this cycle until I have a script so works.

Now consider a script like this one, has Error checking turned on:

<%
Option Explicit

On Error Resume Next

Dim Conn
Dim strSQL

Set Conn = Server.CreateObject ("ADODB. Connection ")
' This DSN does not exist
Conn.Open "Foo"

' ... more code ...

If Err.Number <> 0 Then
Response.Write ("Error number->" & Err.Number)
Response.Write ("<br>error Source->" & Err.Source)
Response.Write ("<br>error Desc->" & Err.Description)
Err.Clear
End If
%>




Viewing the above script through your browser to produce the following output:


Error Number->-2147467259
Error Source-> Microsoft OLE DB Provider for ODBC Drivers
Error Desc-> [microsoft][odbc Driver Manager] Data source name not found and no default Driver specified
To me this information are less useful than the default error message. At least with the "Default error message" I know the "line" on which the error originated. Recently I was has yet another look at the Err object and I stumbled upon something that I ' ve overlooked many times in The past. You can raise your own errors!

The Err object contains a Raise the does exactly this. The Raise method has the following syntax:

Object. Raise (number, source, description, HelpFile, helpcontext)


The technical docs for the Raise can is seen here. A quick Note:when raising a custom error, the error number should be a custom error number plus the constant Vbobjecterro R, to make sure this error number you choose doesn ' t equal a already error number (we LL This in the code below).

An example of using the Raise object to generate we own custom error (with a more descriptive Can be seen below:

1: <%
2:option Explicit
3:on Error Resume Next
4:
5:dim Conn
6:set Conn = Server.CreateObject ("ADODB.") Connection ")
7:
8: ' This DSN does not exist
9:conn.open "Foo"
10:
11:if Err.Number <> 0 Then
12:err.clear
13:err.raise vbObjectError + 7, _
: "Etest.asp", "Connection Open method Failed"
15:end If
16:if Err. Number <> 0 Then
17:response.write ("Error on line->" & Err.number-vbobjecterror)
18:response.write ("<br>error Source->" & Err.Source)
19:response.write ("<br>error Desc->" & Err.Description)
20: