Calculate Sum of Custom Fields for Linked Cards

[Deleted user]

Hey folks,

I'm using Trello to manage home renovation project planning. I have a parent card for each project with a checklist that generates a new linked card each time a task is added (shoutout to Katrin Anger for the rad suggestion in another post!)

Here's the bones of that automation;

when an item is added to checklist "Project Tasks " in a card not in list "Start Here", convert the item to a linked card using pattern "{checklistitem}" copying members, set custom field "Project" to "{triggercardname}", and add an empty checklist named "Sub Tasks" to the card

So, now I have a parent card, say "Water Tanks" and linked cards for tasks, say "Concrete Prep", "Pour Pad", "Install Tanks".

I also have a custom field "duration" that I want to use to calculate project hours (and later to be able to automate timelines using hours and start dates to estimate completion dates).

QUESTION:

How do I set up an automation to calculate for the PARENT card, the sum of the durations of all the linked cards? It's tricky, because the number of linked task cards will vary across projects. I don't know how to write that for an unknown number of linked cards...

The parts are (I think);

• The parent card has the label "PROJECT"
• Each linked task card has the label "Project Tasks"
• Every card related to a project has the custom field "project" populated with the project name, eg "Water Tanks"
• Every card has a custom field "Duration"

What I'd like is something along the lines of;

1. When the custom field "Duration" is updated on a card with the label "Project tasks",
2. calculate the sum of the "Duration" fields on all the cards linked to the parent card (which also has a checklist that has all the linked cards)
3. and populate the "Duration" field on the parent card with that sum.

My strong preference is to use Butler for this, I'm cool to also use powerups, but don't want to use google scripts or other coding solutions (not my bag, and I want to be able to replicate the nuts & bolts of the automation in other contexts)

Thanks for your lovely wise brains!

[Mat]

Hi Tara, 

Thanks for sharing your use case in detail! I can see how useful this workflow is. Right now, Butler/Automation cannot get the value of a custom field from the linked cards back to the "parent" card's custom field. This is a known limitation that we have with our automation. 

If this helps, there is a feature request to have the ability to use the custom field value of a trigger card. Right now, when you use a custom field variable in an action, Butler will only look at the current/parent card. — if there's any additional info or use case that you want to share as to why this feature is important, let me know and I'll pass your information to the relevant team. Otherwise, I'll share your above use case with the team. 

If you are curious about how our team decides which requests we work on, we have published a blog post with detailed information on this process here: https://blog.trello.com/feature-requests-unite-support-and-product

You can find some Power-Ups that can help with your use case here: https://trello.com/power-ups/search?q=custom%20field 

Apologies as I can't help much to give you a better solution but I hope this helps point you in the right direction!