Question

How do we model these objects ?

Scenario 1: Price changes in a time period

EffectiveDate  ExpiryDate    Price
2009-01-01     2009-01-31    800$
2009-02-01     Null          900$

So, if the price changes to 910$ on 2009-02-15, then the system should automatically update the expiry date on the previous effective price to 2009-02-14, to keep it consistent.

Scenario 2: No price specified between 2009-02-01 to 2009-02-28

EffectiveDate  ExpiryDate    Price
2009-01-01     2009-01-31    800$
2009-03-01     Null          900$

So, if new price is specified for 2009-02-15 onwards , then the system should automatically set the expiry date on the record to be inserted to 2009-02-28, because already a record effective from 2009-03-01 exists.

Please suggest an effective way to handle these scenarios to model my framework, or are there any frameworks around that can do this .

Thanks

Answer 1

If a price should always be in effect, then I would use a single column and use queries to determine the expiration.

Create Table Prices
(
    EffectiveDate datetime not null
    , Price decimal(15,4) not null
    , Constraint UC_Prices_EffectiveDate Unique ( EffectiveDate )
)

Select P1.EffectiveDate As Start
    , Coalesce(
                    (
                    Select Min(P2.EffectiveDate) As EffectiveDate
                    From Prices As P2
                    Where P2.EffectiveDate > P1.EffectiveDate)
                    ), '9999-12-31') As End
    , Price
From Prices As P1

This later query you could put in a View so that can easily be used in other queries. If you try to store both the start and the expire, then you need to add a bunch of code, probably in a trigger, than ensures you do not have an overlap nor have a gap.