Make Change to a List of Things using another List of Things

[olivier.cam.n7]

I am creating a basic inventory web app:

I have 3 Things: Article, Delivery, ArticleBuffer, ArticleEnum

Article contains:

• article_name (Text)
• total_quantity (Number)
• list_of_deliveries (which is a list of Things Delivery)

Delivery contains:

• delivery_name (Text)
• list_of_articleBuffer (which is a list of Things ArticleBuffer)

ArticleBuffer contains:

• article_buffer_name (Text)
• quantity (Number)

ArticleEnum contains:

• article_enum_name (Text)

ArticleEnum is used to provide the list of available articles in a Dropdown.

article_name from Article, article_buffer_name from ArticleBuffer, article_enum_name ArticleEnum match when they refer to the same physical article (or object).

I have a Pop up where I can create a new Delivery:

• I fill the delivery_name using an InputField.
• I have a group which can create a new ArticleBuffer. I select from a Dropdown the proper ArticleEnum, it gives my the article_buffer_name. I fill the quantity using another InputField
• I click on a Button, it adds the newly ceated ArticleBuffer to the list_of_articleBuffer of Delivery.

Once the Delivery is properly filled, I want to do this kind of loop:
for ArticleBuffer “ab” inside list_of_articleBuffer of the current Delivery:
for Article “a” inside Article database:
do if (article_buffer_name of “ab”) = (article_name of “a”)
then (total_quantity of “a”) = (total_quantity of “a”) + (quantity of “ab”)

I did not find a way to do this. What am I missing ?