[ZODB-Dev] Find references to an object

[Barry A. Warsaw]

>>>>> "JH" == Jeremy Hylton <jeremy@alum.mit.edu> writes:

>>>>> "GW" == Greg Ward <gward@mems-exchange.org> writes:

    GW> ZODB gurus -- given an OID, is it possible to find all objects
    GW> that reference that object?

    JH> I don't believe any storage has a feature like this.  A
    JH> storage only needs to know about the other direction to do GC.

I believe this is correct.  I don't know of a quick way to find all
the objects that refer to a specific oid.

    GW> Perhaps what I'm looking for is this: a sneaky, underhanded
    GW> way to load object A, find the list of all objects (OIDs) it
    GW> references, and see if object B is in that list.  If so, add
    GW> object A to the list of objects referencing B.  Repeat
    GW> database.objectCount() times.  The problem I see with this is
    GW> how to deal with extension types like BTree, which reference
    GW> lots of objects in an opaque way.

    GW> Any suggestions?

    JH> If you have objects A and B, it should be possible to get a
    JH> list of everything referenced by A and see if B is in that
    JH> list.

This is easier.  Use the storage's load() or loadSerial() method to
get the pickle for the specific oid/version/serialno combination.
Then use ZODB.referencesf.referencesf() to get the list of oids
referenced in that pickle.  E.g.

    from ZODB.referencesf import referencesf
    pickle, revid = storage.load(objAoid, '')
    refdoids = []
    referencesf(pickle, refdoids)
    if objBoid in refdoids:
	blah()

-Barry