Bitemporal data support for the Django ORM.

Any change in an object is implemented in three steps. 1) Invalidate the current row 2) Create a copy of that row with valid_end_date set 3) Create the new row

All Bitemporal objects have a ForeignKey called master to MasterObject, which represents every state the object has been in. To relate to a Bitemporal object you should make another ForeignKey to MasterObject.

Valid Start/End Date

When the record is active in the real world, regardless of the time it was active in the system.

Transaction Start/End Date

When the record was active in the system. Effectively audit columns.

MasterObject Model Methods =========================

get_all():

returns a BitemporalQuerySet containing all versions of the object

get_current():

Short cut for get_all().current().get() - returns a single version of the object

amend(as_of=now(), using=None):

After making changes to a model, call .amend() with an optional as_of date to save the changes as effective on the as_of date. Defaults to the current date and time. using will be passed on to .save().

update(using=None):

After making changes which correct previous errors, call update to save the change while invalidating the previous values. This is equivalent to calling: obj.amend(as_of=obj.valid_start_date) using will be passed on to .save().

save_during(valid_start, valid_end=TIME_CURRENT, using=None):

Save the object in a new row with valid_start_date and valid_end_date set for the provided interval. Existing rows which confict with the vaild period will be updated to have thier end points adjusted.

delete(as_of=now(), using=None):

Will write a new row with the valid_end_date to as_of Returns this new row

The object which delete is called on will be in an inconsistent state after the call to delete.

using will be passed on to .delete().

eradicate():

Call the real delete method, this is hidden since you generally do not want to delete rows.

Manager/QuerySet Methods =============

active():

returns all active rows

current():

returns all current, active rows shortcut for .active().during(now())

during(valid_start, valid_end=None):

If valid_end is None, it will be treated as valid_start + 1ms Return all rows (active or not) that were valid during the interval [valid_start, valid_end)

active_during(txn_start, txn_end=TIME_CURRENT):

If txn_end is None, it will be treated as txn_start + 1ms Return all rows that were active during the interval [txn_start, txn_end)

active row

Any row where txn_end_date is TIME_CURRENT is active.

current row

Any row where valid_start_date < now() and valid_end_date > now()

Temporal consistency invariant

For a given id value and date, there should be a single object identified by its row_id for which date is in the interval [valid_start_date, valid_end_date) and the txn_end_date == TIME_CURRENT