Modeling a cellphone bill: should I use single-table inheritance or polymorphic associations?

Posted by Horace Loeb on Stack Overflow See other posts from Stack Overflow or by Horace Loeb
Published on 2010-04-14T01:50:03Z Indexed on 2010/04/14 1:53 UTC
Read the original article Hit count: 391

Filed under:

ruby

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ruby-on-rails

|

single-table-inheritance

|

polymorphic-associations

In my domain:

Users have many Bills
Bills have many BillItems (and therefore Users have many BillItems through Bills)
Every BillItem is one of:
- Call
- SMS (text message)
- MMS (multimedia message)
- Data

Here are the properties of each individual BillItem (some are common):

alt text

My question is whether I should model this arrangement with single-table inheritance (i.e., one "bill_items" table with a "type" column) or polymorphism (separate tables for each BillItem type), and why.

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