Cferror doesn't process

Question

can anyone tell me if there's anything wrong with this code :
( the bb is set wrong to throw the error )
<cffunction name="onRequestStart" returntype="void"
output="true">
<cfset request.dsn = "codelib">
<cfset request.dbp = "">
<cfset request.dbu = "">
<cfinclude template="header.cfm">
<cftry>
<cfquery name="qDatabase" datasource="#request.dsn#"
maxrows="1">
SELECT
bb
FROM genericdata
</cfquery>
<cfcatch type="database">
<cferror type="exception" mailto="#admin_email#"
template="error.cfm">
</cfcatch>
</cftry>
</cffunction>
i never get the error.cfm page . The query fails and it just
goes displays the page anyway with header and footer. it's as
though it's not being caught or something. I've tried with both
type="exception" and "request"
Thx

Answer 1

> i never get the error.cfm page .
'Course, you don't. There are 2 reasons.
One, when an exception occurs, the try/catch mechanism and
the onError() event override the cferror tag, in that order.
Second, the cferror tag only registers an error that occurs
after the tag. Hence the general advice to let Coldfusion
read the tag as early as possible during a request.
Putting the two together, you can see why you get the result
you get. The error in the query causes execution to move into the
cfcatch block. However, still within the cfcatch block, there is no
code after the cferror tag, hence no exception for the cferror tag
to handle.
If you comment out the onError method and use the following
code, Coldfusion will take you to the error.cfm page. Nevertheless,
I cannot think of a reason why you would want to handle errors in
this way.
<cftry>
<cfthrow>
<cfcatch type="any">
<cferror type="exception" mailto="#admin_email#"
template="error.cfm">
<cfquery name="qDatabase" datasource="#request.dsn#"
maxrows="1">
SELECT bb
FROM genericdata
</cfquery>
</cfcatch>
</cftry>