ExpressionEngine’s Deny Duplicate Data Preference

Posted March 10, 2010 @ 10:51 PM, by Marc, in Client, ExpressionEngine — 1

There’s a preference in the ExpressionEngine control panel called Deny Duplicate Data which, if turned on, will instruct EE to check if new content submitted by a user is a duplicate of existing content already in the database. It’s a moderately helpful measure in the fight against comment spam, but it recently was the cause of a minor client work-flow issue and it succeeded in confusing me for about fifteen minutes before I finally realized that this preference was the culprit. I thought it would be wise to write this blog entry in case it happens to me again, or if anyone is searching the web looking for a solution to this same dilemma.

Deny Duplicate Data Specifics

Before I dive into my client’s work-flow issue and how the Deny Duplicate Data preference was the cause, I’d like to give some specifics about the preference itself.

An explanation from the ExpressionEngine documentation:

Deny Duplicate Data: This option prevents data submitted by users (such as comments or trackbacks) from being processed if it is an exact duplicate of data that already exists. This setting is designed to deter automated spam attacks as well as multiple accidental submissions.

Where you can find this feature within the EE control panel:

In EE version 1.6.x: Admin > System Preferences > Security and Session Preferences, and it’s the fourth preference in the list
In EE version 2.x.x: Admin > Security and Privacy > Security and Sessions, and it’s the fourth preference in the list

How My Client Uses ExpressionEngine

I built an internal requisition system for a client that allows members of the staff to log in and make a wide range of requests that the management have to then read, comment on, and ultimately fulfill.

When a staff member uses the system to request something, the system automatically notifies the folks in management allowing them to quickly jump into the ‘ticket,’ add a comment to let the staff member know what they might expect, and begin doing whatever is necessary to fulfill the request. When the folks in management fulfill the request, whatever it may be, they then log back into the system and mark the ticket as complete.

What My Client Saw and How We Solved the Issue

My client called me the other day and said, “You know, every once in a while I’ll get an error message when I attempt to submit a comment on a ticket.” I asked him what the error message was and what particular steps he was taking that led to the appearance of the error message. He told me that the error message was “Unable to receive your comment at this time,” and that the steps he was taking were:

Log into the system
Click any ticket marked as New
Read the request
Start typing a comment in response
Press submit, and this is when he saw the error message

If I were a smarter person than I actually am, I would have first searched through the ExpressionEngine Knowledge Base for the error message, which would’ve led me to this particular article. Alas, I’m not a very smart person, so I spent ten to fifteen minutes attempting to recreate the error message using my own credentials, then his particular credentials, etc. Wouldn’t you know that every time I entered a test comment hoping to see this elusive error message, I entered a unique comment such as test comment, or another test comment, or even weird, I’m not seeing the error message… If I had only typed the same exact comment more than once, it would’ve immediately appeared.

In the end, I finally searched the EE Knowledge Base for the error message and came up with the page I linked to above. I called my client back, asked him if he could recall typing the same exact comment more than once, and he said that it was entirely possible—especially for the occasional request that warranted a quick comment such as “Thanks, I’m working on it.”

Before turning the Deny Duplicate Data preference off, I attempted to post the same comment twice and low and behold, there was the error message. I entered the control panel, found the preference, turned it off, and attempted to post the same comment twice again. ExpressionEngine didn’t give the error message and it allowed the second comment to be posted. I called my client back, explained to him why he occasionally got that error message in the past, mentioned that I turned the preference off, and reassured him that he would no longer be hassled when trying to post the same comment twice.

Case closed.