Connie's Convenience Store - About Peter Coad

58 Connie’s Convenience Store Applying Patterns: Establish Problem-Domain Responsibilities
Item–line item
Okay. What’s next? How about this:
#9. “Item–Line Item” Pattern transaction patterns
• Typical object interactions
howMany —> getQuantity
calcOverLineItems —> calcForMe rankLineItems —> rateMe
• Examples
(with transaction line items) item–order line item; item–payment line item; item–rental
line item; item–sale line item; item–shipment line item
(with container line items) item–bin line item; item–warehouse line item.
• Combinations
transaction–transaction line item; subsequent transaction–subsequent transaction line
item; transaction line item–subsequent transaction line item; container–container
line item.
For item–sale line item:
– item (collection … of its sale line items)
how much over interval
– sale line item (worker)
how much over interval.
Add services to item and sale line item, and by analogy to cashier, session, and sale
(Figure 1–37):
Cashier
howManyOverInterval
howMuchOverInterval
n
1
Item
name
number
description
price
aboutMe
howMany
rankLineItems
calcOverLineItems
calcForMe
Session
howManyOverInterval
howMuchOverInterval
n 1
n
Sale
howManyOverInterval
howMuchOverInterval
calcSubTotal
n-1
SaleLineItem
howManyOverInterval
calcSubTotal
Figure 1–37: Some pattern instances.
1
quantity
status
aboutMe
LineItem
calcForMe
rateMe
1
1
n
Item
howManyOverInterval