startapp product
create Topic model, and migrate it
register Topic in admin.py
register Topic with TopicAdmin in admin.py
create Source model, and migrate it
add TODO.md
register Source in admin.py
add fields to Source model, and migrate
add SourceAdmin in admin.py, and bind Source model to Topic in admin
organize the order of fields of Source, and migrate it
class Meta in Source model
the draft version of find_max_purchase
the 2nd version of find_max_purchase(), using Decimal class to calculate
fine tune the calc of find_max_purchase() with the calculation on 1st leg and 2nd leg fee
changes on comments
add some conditions on report to find_max_purchase()
change the condition on find_max_purchase()
add Seller model, and migrate it
Bind Seller model to Topic model. Need to alter column `seller` to `seller_id` in db manually
edit TODO. replace the location of Seller model