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Overriding returnFormat at runtime

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Posted in ColdFusion | Posted on 07-03-2008 | 3,238 views

Ok, so this falls in the "Not so sure this is a good idea" department. Stefan Vesterlund posted a comment on my last blog entry concerning returnformat. He asked if it was possible to change the returnFormat at runtime. I said that I didn't think it was possible, but that you could simply use returnFormat="plain" and return JSON or WDDX manually. He played around with it and discovered you could override the default behavior. Consider the following code sample.

view plain print about
1<cffunction name="testMethod" access="remote">
2    <cfset var a = [1,2,4,9]>
3    <cfreturn a>
4</cffunction>

Since I've specified no returnFormat in the cffunction tag, if I hit this via the browser and don't override returnFormat in the query string, the result will be a WDDX string. Now consider this version:

view plain print about
1<cffunction name="testMethod" access="remote">
2    <cfset var a = [1,2,4,9]>
3    <cfif a[1] is 1>
4        <cfset url.returnFormat="json">
5    </cfif>
6    <cfreturn a>
7</cffunction>

The code now checks the first entry in the array, and if the value is 1, it sets url.returnFormat. Surprisingly this works. I guess ColdFusion doesn't bother worrying about the returnFormat settings until the end of the method, which kinda makes sense.

I still feel weird about this one, but thought I'd pass it along.

Comments

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Dave Ferguson said on 07-03-2008 at 8:42 AM #
I could see this as maybe being useful in the sense that you could have a single multiple use function.

--Dave
Raymond Camden said on 07-03-2008 at 8:47 AM #
Well, my issue is that CF already provides a way to override the returnFormat. The client does it (using the query string). This though is all server side.

I don't know - it just feels wrong. :)
John Farrar said on 07-03-2008 at 4:42 PM #
This could be used to make sure the return format isn't altered. (Not that I see a use case issue, but that would be one scenario.)
Steve Ross said on 10-21-2011 at 10:08 AM #
Would this fail if it was an ajax post instead of a get? ie: url variable would be form variable right?
Raymond Camden said on 10-21-2011 at 10:44 AM #
Possibly. Remember when doing a POST you can still send URL params. But yeah - you can change the code to check form instead (or both).

Personally - when I do Ajax hits, I'll put the returnformat and method in the query string:

some.cfc?method=doit&returnformat=json

and use the Form data for my actual data.