How can a checklist item's linked card inherit a field value from the card to which it is linked?

[Andy McAfee]

I am new to Trello, and perhaps this scenario is complex, but I am trying to figure out how to implement an Identifier that links all my dependency tasks to my parent task taking into consideration multiple tiers of dependencies, and I am trying to avoid 3rd party Trello Powerups.

I wanted to architect a dependency system for card relationships, and I found this article which is beneficial:
https://help.trello.com/article/1165-task-dependencies

I have implemented this system successfully, but I would like to take this one step further and introduce a custom field (text field called "Parent Card ID") that stores the card's {cardid}.

Workflow example:
1. Create Parent Card called "Project 1"
2. Populate custom field "Parent Card ID" with {cardid}.
3. Add "Task 1" item to "Sub-tasks" checklist in card "Project 1" and linked card is automatically created.
4. Add "Task 2" checklist item to the "Task 1" card created in Step 3 and linked card is automatically created.

The above scenario illustrates a family tree of dependencies (Parent => Child => Grandchild). All 4 steps are working correctly. My questions are regarding Steps 3 and 4... How can I utilize Butler to populate these dependency cards with the custom field "Parent Card ID" value from the highest level ancestor card?

[milynnus · Accepted solution]

@Andy McAfee 

If you are keen I have a private video that has that working on 3 boards. My contact details are on my profile page. 

It used only Trello automation. 

[Andy McAfee]

@milynnus 

I figured it out! I got the idea from one of your other posts on this Community. Thanks!

I ended up implementing the following commands to accomplish this (perhaps there is a better way?)

1. when the red "Project" label is added to a card without the red "Subtask" label, set the card's description to "{carddescription} \n\n Parent Card ID: {cardid}", and set custom field "Parent Card ID" to "{cardid}".

2. when an item is added to checklist "Sub-tasks", convert the item to a linked card copying labels and members, add the red "Subtask" label to the card, rename the card to "{cardname} - Subtask", lookup the first card linked in the attachments, and set the card's description to "{foundcarddescription}" 

3. when a card with the red "Subtask" label with custom field "Parent Card ID" cleared with a description containing "Parent Card ID: {*}" is added to the board, set custom field "Parent Card ID" to "{wildcard1}"