ZODB: The Z Object Database

[Grant]

The Z Object Database

[http://www.amk.ca/zodb/zodb-zeo.html]

ZODB lets you add persistence to Python objects in an almost completely 
transparent way, giving Python programmers an object database that 
allows making Python objects persistent with very little effort. (The 
"very little effort" part should not be understated. Commercial object 
databases for C++ or Java often require that you jump through some hoops 
and avoid certain data types or code styles. In comparison the 
naturalness of the ZODB is astonishing, and testimony to both Python's 
flexibility and Jim Fulton's skills.)

There are 3 main interfaces in the ZODB: Storage, DB, and Connection 
classes.

* Storage classes are the lowest layer, and handle storing and 
retrieving objects from some form of long-term storage. A few different 
types of Storage have been written, such as FileStorage, which uses 
regular files, and BerkeleyStorage, which uses Sleepycat Software's 
BerkeleyDB 2.7. You could write a new Storage that stored objects in a 
relational database or Metakit file, for example, if you needed to 
ensure some property useful to your application. Two example storages, 
DemoStorage and MappingStorage, are available to use as models if you 
want to write a new Storage.

* The DB class sits on top of a storage, and mediates the interaction 
between several connections. One DB instance is created per process.

* Finally, the Connection class caches objects, and moves them into and 
out of object storage. A multi-threaded program can open a separate 
Connection instance for each thread.