On Sep 19, 2006, at 5:36 AM, Jacopo Cappellato wrote:
David E Jones wrote:
On Sep 19, 2006, at 2:10 AM, Jacopo Cappellato wrote:
On the other hand, the "amount" (that is stored in the
OrderItem.amountSelected field) is used as a multiplier for the
unit price: if a product (with require amount = Y) has a unit
price of 2$ (ProductPrice) and you select an amount of 100 then
the new unit price (in the cart/order) is 200; the "amount" will
not affect in any way the quantity issued from inventory that is
always the OrderItem.quantity field.
Is this correct?
I think this is correct, but unfortunately it is also a bug... The
amount really should be multiplied by the quantity in order to get
the total to deduct from inventory and so on.
Hmmm... but in this way we could have non integer inventory quantities
(since the amount value can be a non integer value)... do we really
want
this to happen?
I think that non-integer inventory quantities are okay, and for some
products they are necessary. In fact, is there any way to avoid this
quite a few manufacturing materials like rope, wire, glue, paint/
lacquer, and so on?
PS: This makes me think that the amount multiplier has some
potential and could be used also to express small unit prices
(amount = 0.0001)... but the problem is that the new unitPrice is
stored in the OrderItem.unitPrice field that has limited
precision... maybe we should store there the original unit price
and just get the order item total as: OrderItem.quantity *
OrderItem.amountSelected * OrderItem.unitPrice
Isn't it done this way already, ie calculating the order item
subtotal this way?
Not exactly in this way.
For example: if I order an item with original unit price of 15.99,
quantity = 2 and amount = 1.5, in the OrderItem entity the
following values are stored:
quantity = 2
selectedAmount = 1.5
unitPrice = 23.98 (!!! This is the result of 1.5 * 15.99 = 23.985)
and the order item subtotal is (correctly) calculated multiplying
the quantity and the unitPrice: 47.96
Maybe we should instead store in the OrderItem:
quantity = 2
selectedAmount = 1.5
unitPrice = 15.99
and the order item subtotal should be calculated multiplying the
quantity, the unitPrice and the selected amount: 2 * 1.5 * 15.99 =
47.97
But then the selectedAmount should be displayed in all the order
view screens.
Should we try to clean/fix this?
If so, I could put some effort in this but first I'd like to be
sure to understand the intended use of the amount field.
This is interesting, and a little scary... ;)
I've never actually looked into this in detail as Andy is the one who
implemented it. I don't think I like this implementation decision
though, so unless someone sees a reason why it would be better this
way I think we should change it. I _can_ think of a couple of reasons
why it is worse: it is not very intuitive, and it could lead to
inaccurate price calculations.
-David
