Use order numbers to guide deduplication

[michielbdejong]

If you order an item from mobile and then order the same item from desktop, how many should be ordered? Should these be deduplicated or not?

In the latest strawman implementation (86fde5f) these are never deduplicated, if there are two separate 'add quantity' user interactions, then these will add up.

However, it may be more intuitive to say that within one invoice id, you never 'add' quantity of an item, but instead 'set' quantity of an item.

If you want to buy 2 cans of paint for the shed and another 2 cans of paint for the fence, then you should open two separate orders (invoices), and if you still edited the same invoice from two devices can then be interpreted then maybe we can assume that you're talking about the same two cans in both GUI interactions?

An even beter UX might be if you specify the purpose, so:
From mobile:

• operation: 'set quantity needed'
• product: 'cans of paint',
• amount: 2
• purpose (note to self): 'for shed'

From desktop:

• operation: 'set quantity needed'
• product: 'cans of paint',
• amount: 2
• purpose (note to self): 'for fence'

From desktop:

• operation: 'set quantity needed'
• product: 'cans of paint',
• amount: 3
• purpose (note to self): 'for shed'

End result: 5 cans of paint (3 for shed, 2 for fence)

[michielbdejong]

A simpler version of this, for now, is to change the three 'add' operations to absolute value-setting operations, and last write (according to wall clock, with a random hash as a tie-breaker) wins.