Database Trigger - Difference between 2 lists


I want to activate a database trigger when 2 lists change.

John and Tom are assigned a job. The manager changes the assignment to John and Fiona. I want to use the database trigger functionality to kick off a workflow.

I am currently using the following:


I only found out recently it doesn’t work for 100% situations.

OK scenarios (changes, additions)
John & Tom → John & Fiona or John & Tom → Frank & Fiona
John → Tom
John → John & Tom
Empty → John

Where it doesn’t work (reductions)
John & Tom → John
(This returns 1 = 1)

I also looked at Merge but then the addition situation doesn’t work

Any ideas?

Hi there, @jeffrey.j.obrien… I could be way off base (and maybe I am just biased against database triggers because the most badass CTO I’ve ever worked with hated them for some reason), but why do you need a database trigger here? I assume the process by which a manager changes a job’s assignment is well-defined, so can’t you just have a workflow that changes the assignment to the appropriate people when the manager makes the change? It seems to me like it should be super straightforward, but again, I could be (and likely am) missing something.


The assignment is updated along with a load of other things - about 10 fields altogether.

So, I only want the workflow to run if the list in the assignment field has changed.

I assume I would have the same issue in a workflow on the front end trying to figure out if the assignment is different.

I just did some testing (although, admittedly, not with a database trigger), and it looks the example I made covers all of the scenarios by using the :minus list operator. Oh, and I also have the experimental parentheses feature enabled (which encloses everything before the :count operator in parentheses), so I don’t know if that would make a difference.

Give this a shot… Work Order Before Change's Assigned User:minus list Work Order Now's Assigned User:count is not empty.

Again, a similar expression appears to work in all scenarios for me, but I have it as a condition on a workflow event as opposed to using it in a database trigger.

Thanks for all your help on this. I tried your suggestion and most scenarios work.

Screenshot 2023-01-02 at 16.10.31

When the before list equals the after list (No change) the workflow still fires.

I also turned on experimental parenthesis and it made no difference.

Can you confirm no change still fires the workflow for you…?

Aw, crap… I was so focused on making sure the lists changed appropriately, I forgot to make sure the workflow didn’t run if the lists are the same… and it does run, as you pointed out. Sorry about that… I will keep playing around with it.

I have been playing around with this one pretty much since my last reply, and that’s just sad when it turns out the answer might be quite simple.

If the expression in your original post was working in all cases except for John & Tom → John, then adding an or after your expression and checking to see if the count of the first list is not equal to the count of the second list should do the trick because if the count of items in each list is not the same, then the lists can’t contain the same items.

So, in the end, I believe your expression would be…

Work Order Before Change's Assigned User intersect with Work Order Now's Assigned User:count is not Work Order Now's Assigned User:count or Work Order Before Change's Assigned User:count is not Work Order Now's Assigned User:count

I tested every scenario in my sample project (including making sure the workflow doesn’t run if the lists are the same), and it appears to work as expected.


That worked. It now covers all the scenarios.

Thanks for all your help.

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sorry to revive old thread but I was looking for a solution for this buried somewhere else and

Trigger only when:
Thing before change’s List:format as text is not Thing now’s List:format as text

i use unique ids for each item and . as the delimiter. So I think it will work with a single expression like this