Handling unknown events in Model-Glue

November 5, 2006 coldfusion

(This post is more than 2 years old.)

What happens in a Model-Glue application when you pass in an unknown event? An error is thrown. While this makes sense - it may not be desired behavior for an application. For example - I'd probably consider most unknown events to be 404 errors. So how can you handle it?

Model-Glue lets you define the event to fire when an error occurs. In Model-Glue: Unity you can find this setting in the ColdSpring.xml file


<property name="defaultExceptionHandler"><value>exception</value></property>

The "out of the box" exception event in Model-Glue prints out a few pieces of information from the exception. Obviously you wouldn't have that on a live site. Normally I simply take the exception and mail it to myself (along with the form, url, and session scopes).

So how did I handle the unknown event? The first thing I did was dump the exception that Model-Glue was throwing. I was hoping a certain code would be thrown, but the only information I could use was the exception message. It was in this form:

Model-Glue: There is no known event handler for "x".

So I first added this to my exception file:


<!--- 
Look for event handler missing.
--->
<cfif findNoCase("Model-Glue: There is no known event handler for", exception.message)>
	<cflocation url="/">
</cfif>

When this didn't work - I did a quick view source and discovered there were two spaces between Model-Glue: and the message. So I quickly changed it to:


<!--- 
Look for event handler missing.
--->
<cfif findNoCase("Model-Glue:  There is no known event handler for", exception.message)>
	<cflocation url="/">
</cfif>

Obviously you should consider doing more than just sending the user away. You could log the event to the database and see if there is a particular event being called multiple times.

You could also use logic to check for typos or commonly mistyped URLs. For example - someone keeps trying to load the event, "page.rss/", at RIAForge. Notice the / at the end? I whipped up this code to handle it:


<cfif findNoCase("Model-Glue:  There is no known event handler for", exception.message)>
	<cfset unknownEvent = rereplace(exception.message, ".*""(.*?)"".*", "\1")>
	<cfif unknownEvent is "page.rss/">
		<cflocation url="#viewState.getValue("myself")#page.rss" addToken="false">
	<cfelse>
		<cflocation url="/">
	</cfif>
</cfif>

By the way - I bugged Joe to consider adding a "Unknown Event" configuration setting to the framework.