Cross Libraries Operations
I Think it would be very beneficial to have fields perform operations on other libraries (at least the basic add/subtract operations).
For example:
Library 1 contains customer orders.
Library 2 contains products.
Library 1 links to products on Library 2 and each time this is done Library 2 subtracts a product from the quantity field.
Library 1 has also a field that specifies how many products client X purchased.
I assume this is a VERY common scenario for databases. I would be good to be included on Memento.

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Winston C.Hurchill commented
6 years later how is this planning. It is a delicate novelty. Because it can create problems. but it would be great
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roberto dal maso commented
This would be a feature I need too, but I agree with Pete
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Pete commented
This feature could be useful and dangerous. When does it "subtract"? How do you "restock"? how does this deal with synced libraries? This is usually done with views or more advanced query systems that full-scale databases have (server will search "orders" for individual instances that subtract or add to a specific "product"s quantity and compile that number every time the quantity of the product is requested) I think it's kinda like "journalling" in filesystems? I could be wrong. Point is that it might be outside the scope of this size / style database (Memento).
It would be nice if the "link to entry" system did have a way to specify a "quantity" of the linked entry that could represent how many of linked product was included on a specific order in an "Orders" Library... But that could be just as bad, I really don't know much about programming a database app.