Ask a Jedi: UDFs and CFCs

Sorry for the light ColdFusion content this week. As you can tell, I’m really getting into Flex 2. Anyway, here is an interesting question from Todd:

Can you clarify how/when/if it is appropriate to use/not use a UDF within a CFC? Any thoughts on the topic? I've seen a lot of conflicting opinions on the topic and I was hoping you could clarify. Would it be better to just convert the UDF to a CFC and call that CFC from another CFC? Are there best practices surrounding this topic?

So first off, let’s clarify something. A CFC is a collection of methods, normally written using the cffunction tag. A UDF can be written the same way. So to be precise, your question involves the use of “general purpose” routines for a CFC. Here is an example: I have a CFC that abstracts a bank account. I have another CFC that abstracts a bank customer. It just so happens that both CFCs have a need for a utility method called paragraphFormat2 . How would you add this code to your two CFCs?

One option is to simply cut and paste the cfscript into the CFC. This works (but is a bit ugly). Of course, if you find a bug in the UDF, you then need to duplicate the fix amongst multiple CFCs. You could use a cfinclude instead of course. However another problem is that the UDF will be available outside of the CFC as a public method. The cfscript format for UDFs doesn’t allow for access permission changes.

So what do I do? Normally I do exactly what you suggested. I create a CFC called “Utils” to store my UDFs. I then create an instance of this CFC inside my other CFCs. You can see this in BlogCFC and Canvas as well as other of my projects.

Along with including the “Utils” CFC in my CFCs, I’ll also put a copy of the CFC in the Application scope. This way I can use the UDFs in normal CFML pages as well. (As just an FYI, if for some reason you are still on CF5, Adobe recommends against storing UDFs in the shared scopes.)

Is this best practice? I would say so. But as always, my readers are nice and diverse, so please chime in.

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