Dieter Maurer skrev:
Chris S wrote at 2006-9-3 15:40 -0400:
Is there a standard procedure for dealing with fundamental changes to
classes? For instance, how do you make a ZODB cope with a class being
renamed, or being placed in a different location? How will it know
that oldmod.myclass == newmod.myclass?
It does not.
You can use so called "module aliases" to partially cope
with module relocation and "class aliases" to cope with class renaming.
Otherwise, you have to use migration scripts that physically
recreate the objects (and the references to it!) with the new classes.
It does too! :-) (In a fashion)
You implement your own classFactory method and set that to be the DB
instance's classFactory.
If you then load all the objects in the database, you can map
modulename, globalname to the new location and return the correct
classes. If you also mark every object as changed and then commit the
transaction all the invalid modulename, globalnames are updated to the
new location in your source.
ex sketch:
In migration script
from ZODB.broken import find_global, Broken
def myClassFactory(connection, modulename, globalname):
# simplified, without error checking
theGlobal = find_global(modulename, globalname)
if issubclass(theGlobal, Broken):
newModulename, newGlobalname = translateLocation(modulename,
globalname)
theGlobal = find_global(newModulename, newGlobalname)
return theGlobal
def translateLocation(modulename, globalname):
# perhaps have a dictionary mapping tuples of old modulename,
globalname to a tuple of new modulename, globalname.
# a version integer in the root can help performing the correct
mappings in case you've done a back and forth rename and want to support
converting databases from several different version.
db = DB(someStorage)
db.classFactory = myClassFactory
conn = db.open()
for each in ZodbIterator(conn)
each._p_activate()
each._p_changed = True
transaction.commit()
The ZodbIterator class is something I stole from someone and modified a bit.
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