the issue of extracting data from parent and child tables.

I created a "Not showing" button in the "Repeat code" and "Random code" tables. I want it to be able to distinguish between several display conditions. If it is turned on, it will not be displayed in the "Preview". How should I write the code for "Preview"?

You can filtering:

join(Products.'Random code'['Not showing' = false].'文本', ", ") + "   " +
join(Products.'Repeat code'['Not showing' = false].'文本', ", ")

The "Orders" table has a one-to-many relationship with the "Products" table.Every time I add a child record, I need to click "Add existing". If I need to add them in bulk, is there a better and faster way?

This one is a bit trickier to explain. I've attached a DB that does something like you want.

In the Pre-Production tab of the Dashboard you can select an Article then type in how many you want to build in "How many in this run?" and then click on Create Run and it will create records in Production.

In the Production tab, you can select record(s) in Pre-Production Runs then click on Run Selected and it will modify the selected records, while doing other things.

In the Post-Production tab, you can see at the bottom a dynamic choice field that you can select a run then type in a "New Quantity" and it will modify the selected record.