API

Currently, there are the utilities: getHistory(obj, first=0, last=20), getObjectAt(obj, time), generateHistory(obj) and generateBTreeHistory(btree).

time can be a Zope DateTime instance, a float in seconds since epoch or a serial/transaction id.

generateHistory is a generator version of getHistory.

While generateHistory(btree) reports only changes to the top level btree object, generateBTreeHistory combines the history for all (current) subtrees and subbuckets, i.e. it treats the btree as the application sees it and not on the persistence level only. Note that the history records generated by generateBTreeHistory may not be complete: some deletion operations may be missing. However, there will be at least one entry in the history refering to such deletions.

Usage example

In the example below, the ZODB contains a folder f. Let’s have a look at its history.

>>> from dm.historical import getHistory, getObjectAt
>>> from pprint import pprint as pp
>>> h = getHistory(f)
>>> pp(h)
[{'description': '',
  'obj': <Folder at /f>,
  'size': 157L,
  'tid': '\x03r\xc8\x1b\xf3hhU',
  'time': DateTime('2008/01/01 09:59:57.049 GMT+1'),
  'user_name': '',
  'version': ''},
 {'description': '',
  'obj': <Folder at /f>,
  'size': 124L,
  'tid': '\x03r\xc8\x1bX\x0e\xfb\xcc',
  'time': DateTime('2008/01/01 09:59:20.639 GMT+1'),
  'user_name': '',
  'version': ''},
 {'description': '',
  'obj': <Folder at /f>,
  'size': 48L,
  'tid': '\x03r\xc8\x15\x1c\x9f\xb03',
  'time': DateTime('2008/01/01 09:53:06.709 GMT+1'),
  'user_name': '',
  'version': ''}]

This tells us that the ZODB knows about 3 transactions affecting f. We can access its state after the first transaction.

>>> f1 = h[-1]['obj']
>>> f1.objectIds()
[]

f was empty at that time. Let’s see how f was changed by the other transactions:

>>> for hr in h:
...   print (hr['time'].strftime('%H:%M:%S'), hr['obj'].objectIds())
...
09:59:57 ['x', 'y']
09:59:20 ['x']
09:53:06 []

This tells us that the second transaction added x and the third transaction y.

We can control which history records are retrieved with the optional parameters first and last.

>>> pp(getHistory(f,last=1))
[{'description': '',
  'obj': <Folder at /f>,
  'size': 157L,
  'tid': '\x03r\xc8\x1b\xf3hhU',
  'time': DateTime('2008/01/01 09:59:57.049 GMT+1'),
  'user_name': '',
  'version': ''}]
>>> pp(getHistory(f,first=2))
[{'description': '',
  'obj': <Folder at /f>,
  'size': 48L,
  'tid': '\x03r\xc8\x15\x1c\x9f\xb03',
  'time': DateTime('2008/01/01 09:53:06.709 GMT+1'),
  'user_name': '',
  'version': ''}]

getObjectAt can be used to retrieve the historical state at a given time. Say, we want to learn how f was at 9:55. The most easy way to specify a time is via a DateTime.

>>> from DateTime import DateTime
>>> dt=DateTime(2008,1,1,9,55)
>>> dt
DateTime('2008/01/01 09:55:00 GMT+1')
>>> getObjectAt(f, dt).objectIds()
[]

When we request the state beyond the ZODB’s maintained history, we get a POSKeyError.

>>> getObjectAt(f, DateTime(2008,1,1,9,50))
Traceback (most recent call last):
  ...
ZODB.POSException.POSKeyError: ('\x00\x00\x00\x00\x00j\x82\xd3', '\x03r\xc8\x12\x00\x00\x00\x00')

The time can also be specified via a float in the unit seconds since epoch or via a serial/tid. However, these will be used rarely.

>>> ts=dt.timeTime()
>>> ts
1199177700.0
>>> getObjectAt(f, ts).objectIds()
[]
>>> getObjectAt(f, b'\x03r\xc8\x15\x1c\x9f\xb03').objectIds()
[]

Dependencies

This package depends on a ZODB variant (ZODB or ZODB3, maybe others) and DateTime.

History