Element col1 is undefined in CFML structure

In most cases, you do know what struct-keys to expect.  When you don't, you can usually get what you want by <cfloop>ing over the structure itself.  You can also, of course, obtain a list of the keys.

To handle the case of bumping into a struct-key that doesn't exist, well, you've got two good choices ... depending on how probable you consider the event to be, and/or if the presence or absence of a key "means something."

1. The key-exists function will tell you if "the bridge is out" so that you don't wander over a precipice.  The "tradeoff," theoretically at least, is that you are probing the structure for key-existence twice in a row.  Now, hash-lookups are extremely fast by their nature, and the CF/Java implementation is known to be "good."
2. Exception-catching via <cftry> is another viable choice.  I happen to prefer to put such a block around everything, so that my app doesn't "lose face" if when something happens to go wrong, but exceptions do have a place in ordinary procedural logic.  You simply place a nice comfortable trampoline under the bridge, then charge right across it.  Most of the time the bridge holds-up just fine and you haven't wasted any time checking the floorboards.  When something "exceptional" does occur, however, you fall through the deck, land harmlessly on the trampoline and "respond appropriately."  If you find yourself in the exception-handler, you know that whatever you were looking for just happened.
   

It all pretty-much coms down to your personal preference, because ColdFusion is typically not used to handle computationally-intensive nor time-consuming work.  Whatever makes your code cleanest and most-reliable is the path that you should take.

1. Use StructKeyExists to check for the key before using it

or

2. Use cftry in combination with cfcatch around the code that

generates the error.

In 99% of the cases I've used StructKeyExists to check if the key

exists (catching an error is more expensive and doesn't allow you to

control the flow of the code in the same way as StructKeyExists).

Mack