zc.beforestorage 0.2.0

Change history

0.1.1 (2008-02-07)

Fixed a packaging bug that caused some files to be omitted.

Using ZConfig to configure Before storages

To use before storages from ZConfig configuration files, you need to import zc.beforestorage and then use a before storage section.

>>> import ZODB.config
>>> storage = ZODB.config.storageFromString("""
...
... %import zc.beforestorage
...
... <before>
...     before 2008-01-21
...     <filestorage>
...         path my.fs
...     </filestorage>
... </before>
... """)

>>> storage
<Before: my.fs before 2008-01-21 00:00:00.000000>

>>> storage.close()

If we leave off the before option, we’ll use the current time:

>>> storage = ZODB.config.storageFromString("""
...
... %import zc.beforestorage
...
... <before>
...     <filestorage>
...         path my.fs
...     </filestorage>
... </before>
... """)

>>> storage
<Before: my.fs before 2008-01-21 18:22:49.000000>

>>> storage.close()

We can also give the option ‘now’ and get the current time.

>>> import ZODB.config
>>> storage = ZODB.config.storageFromString("""
...
... %import zc.beforestorage
...
... <before>
...     before now
...     <filestorage>
...         path my.fs
...     </filestorage>
... </before>
... """)

>>> storage
<Before: my.fs before 2008-01-21 18:22:53.000000>

>>> storage.close()

We can give the option ‘startup’ and get the time at startup.

>>> import ZODB.config
>>> storage = ZODB.config.storageFromString("""
...
... %import zc.beforestorage
...
... <before>
...     before startup
...     <filestorage>
...         path my.fs
...     </filestorage>
... </before>
... """)

>>> storage
<Before: my.fs before 2008-01-21 18:22:43.000000>
>>> import zc.beforestorage
>>> import ZODB.TimeStamp
>>> print str(ZODB.TimeStamp.TimeStamp(zc.beforestorage.startup_time_stamp))
2008-01-21 18:22:43.000000
>>> storage.close()

Demonstration (doctest)

Note that most people will configure the storage through ZConfig. If you are one of those people, you may want to stop here. :) The examples below show you how to use the storage from Python, but they also exercise lots of details you might not be interested in.

To see how this works at the Python level, we’ll create a file storage, and use a before storage to provide views on it.

>>> import ZODB.FileStorage
>>> fs = ZODB.FileStorage.FileStorage('Data.fs')
>>> from ZODB.DB import DB
>>> db = DB(fs)
>>> conn = db.open()
>>> root = conn.root()
>>> import persistent.mapping

We’ll record transaction identifiers, which we’ll use to when opening the before storage.

>>> import transaction
>>> transactions = [root._p_serial]
>>> for i in range(1, 11):
...     root[i] = persistent.mapping.PersistentMapping()
...     transaction.get().note("trans %s" % i)
...     transaction.commit()
...     transactions.append(root._p_serial)

We create a before storage by calling the Before constructer with an existing storage and a timestamp:

>>> import zc.beforestorage
>>> b5 = zc.beforestorage.Before(fs, transactions[5])
>>> db5 = DB(b5)
>>> conn5 = db5.open()
>>> root5 = conn5.root()
>>> len(root5)
4

here we see the database as it was before the 5th transaction was committed. If we try to access a later object, we’ll get a POSKeyError:

>>> conn5.get(root[5]._p_oid)
Traceback (most recent call last):
...
POSKeyError: 0x05

Similarly, while we can access earlier object revisions, we can’t access revisions at the before time or later:

>>> _ = b5.loadSerial(root._p_oid, transactions[2])

>>> b5.loadSerial(root._p_oid, transactions[5])
Traceback (most recent call last):
...
POSKeyError: 0x00

>>> conn5.get(root[5]._p_oid)
Traceback (most recent call last):
...
POSKeyError: 0x05

Let’s run through the storage methods:

>>> b5.getName()
'Data.fs before 2008-01-21 18:23:04.000000'

>>> b5.getSize() == fs.getSize()
True

>>> for hd in b5.history(root._p_oid, size=3):
...     print hd['description']
trans 4
trans 3
trans 2

>>> b5.isReadOnly()
True

>>> transactions[4] <= b5.lastTransaction() < transactions[5]
True

>>> len(b5) == len(fs)
True

>>> p, s1, s2 = b5.loadBefore(root._p_oid, transactions[5])
>>> p == fs.loadSerial(root._p_oid, transactions[4])
True
>>> s1 == transactions[4]
True
>>> s2 is None
True

>>> p, s1, s2 = b5.loadBefore(root._p_oid, transactions[4])
>>> p == fs.loadSerial(root._p_oid, transactions[3])
True
>>> s1 == transactions[3]
True
>>> s2 == transactions[4]
True

>>> b5.lastTid(root._p_oid) == transactions[4]
True

>>> b5.new_oid()
Traceback (most recent call last):
...
ReadOnlyError

>>> from ZODB.TimeStamp import TimeStamp
>>> b5.pack(TimeStamp(transactions[3]).timeTime(), lambda p: [])
Traceback (most recent call last):
...
ReadOnlyError

>>> b5.registerDB(db5)

>>> b5.sortKey() == fs.sortKey()
True

>>> b5.tpc_begin(transaction.get())
Traceback (most recent call last):
...
ReadOnlyError

>>> b5.store(root._p_oid, transactions[4], b5.load(root._p_oid)[0], '',
...          transaction.get())
... # doctest: +ELLIPSIS
Traceback (most recent call last):
...
StorageTransactionError: ...

>>> b5.tpc_vote(transaction.get())
... # doctest: +ELLIPSIS
Traceback (most recent call last):
...
StorageTransactionError: ...

>>> b5.tpc_finish(transaction)
... # doctest: +ELLIPSIS
Traceback (most recent call last):
...
StorageTransactionError: ...

>>> b5.tpc_transaction()
>>> b5.tpc_abort(transaction)

Before storages don’t support undo:

>>> b5.supportsUndo
Traceback (most recent call last):
...
AttributeError: Before instance has no attribute 'supportsUndo'

(Don’t even ask about versions. :)

Closing a before storage closes the underlying storage:

>>> b5.close()
>>> fs.load(root._p_oid, '')
Traceback (most recent call last):
...
ValueError: I/O operation on closed file

If we ommit a timestamp when creating a before storage, the current time will be used:

>>> fs = ZODB.FileStorage.FileStorage('Data.fs')
>>> from ZODB.DB import DB
>>> db = DB(fs)
>>> conn = db.open()
>>> root = conn.root()

>>> bnow = zc.beforestorage.Before(fs)
>>> dbnow = DB(bnow)
>>> connnow = dbnow.open()
>>> rootnow = connnow.root()

>>> for i in range(1, 11):
...     root[i] = persistent.mapping.PersistentMapping()
...     transaction.get().note("trans %s" % i)
...     transaction.commit()
...     transactions.append(root._p_serial)

>>> len(rootnow)
10

The timestamp may be passed directory, or as an ISO time. For example:

>>> b5 = zc.beforestorage.Before(fs, '2008-01-21T18:23:04')
>>> db5 = DB(b5)
>>> conn5 = db5.open()
>>> root5 = conn5.root()
>>> len(root5)
4

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