Multiple rows insertion

Need some help finding a solution for this.
I have a few tables:
3 related tables for “Templates” and their items.
I need a screen in which the user selects a template for a customer
and then to populate a new table with data from the Templates tables and the selected CustomerID.

  1. I don’t know up front how many rows will be in each template.
  2. I cant use add row action because it could be up to 100 rows at a time.
  3. I cant base on relation lookups because the data in the new table needs to me modified by the user and is not for display only.

I am thinking about something like within google sheets that is triggered when a new row is added to the Customer+Template combination and selects the data using a query and inserts it, but it gets complicated if he needs to delete it.

also thought about doing something with checklists but couldn’t figure it out since I will eventually have the same problem inserting blocks of data in actions. There is no custom action on the “Checked” click itself and to insert each row independently the user will have to click up to 100 rows…

I haven’t used user specific columns yet.
Could that be a solution if the user that modifies the template for the customer is not the customer himself that is logged in?

I would also love getting some new ideas…

It can be done using integromat. You can play with goolge sheet, csv create and parse.

I’m using it for uploading bulk data to sheets from glide itself.