Help with nested/matrix sum/product expression?

[Aurelien]

Hi AppSheet Community,

I’m struggling with an expression, I don’t know how to make it.
I hope you will find out !

Situation:
I have basically an inventory app.
The particularity is that some items can be made of others.
For example :

• window panes
• shower kits, each made of 3 window panes and 2 taps

→ How to calculate the virtual total stock of window panes ?

Structure:

• Products Table
• LineItem_Pdt Table
  
• AssemblyPart Table
  

Visual example:

My first thought was to try a matrix product, but I didn’t find a way to do so with AppSheet. I assume I should use some additional virtual column, but I don’t see how.

Thank you in advance for your help, you expressions-masters !