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Kirill Smelkov
Zope
Commits
9b37bd15
Commit
9b37bd15
authored
Jul 23, 1999
by
Jim Fulton
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The Zope Object Database, ZODB, version 3.0
ZODB is the next generation of our object database architecture.
It provides a number of advantages over or existing databases:
- Support for concurrency,
- Well-defined storage management interface that will allow many
different storage management strategies to be used, from file
storage, to RDBMS storage, to memory storage,
- More robust file storage format,
- Much better version support and integrations of
versions with the transaction system. For example,
it is possible to commit from one version to another,
to undo version commit and abort, and to use "temporary
versions" to reduce memory use when manipulating large
quantities of data.
- Support for multiple databases in the same object system.
- Support for multi-process storage managers, although the
standard distribution will not include any multiple process
storage managers.
Note: Using ZODB 3 from Python
In ZODB 2, you could access the top-level application object
with::
import Main
app=Main.app
You could then navigate from the top-level object by getting
attributes, calling methods, etc..
In ZODB 3, you get the top-level object like this::
import Zope
app=Zope.app()
... do stuff with objects
# and when you're done:
app._p_jar.close()
You have to import the Zope application module, which uses
ZODB 2 rather than ZODB 2. In ZODB 3, you have to get a
connection to a database before you access an object. The
'app()' function combines opening a connection and getting the
top level object. When your done using the top-level object
(or any objects accessible from it) you can close the database
connection by calling the 'close' method on the '_p_jar'
attribute, which is the database connection. You don't need
to close the connection if you are going to exit Python
without doing any more work.
Don't forget to::
get_transaction().commit()
If you want any changes to made to be saved.
Note: Converting ZODB 2 (aka BoboPOS) data files to ZODB 3.
The bbb.py script in utilities can be used to convert data
files from ZODB 2 to ZODB 3 format::
utilities/bbb.py -f output_file input_file
Here's a example::
utilities/bbb.py -f var/Data.fs var/Data.bbb
You can also convert export files from ZODB 2 by inclding the
-x option::
utilities/bbb.py -x -f output.zexp input.bbe
ZODB 3 and Zope Database Adapters
Most database adapters are *currently* likely to be problematic unless
the underlying extensions and libraries:
- allow multiple simultaneous database connections,
- are thread safe,
- give up the Python global interpreter lock when
making database calls.
This is only a problem when running Zope 2 with multiple
threads.
ZODB 3 Futures
These are features that are lkely to wait for releases after 2.0.
- Multiple database support
- OPTIMIZATION: FileStorage will get a more efficient data
structure for maintaining index information and key methods
in the ZODB framework will move to C.
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