-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 01/22/2011 08:54 AM, frits.swinkels wrote: > I am new to ZODB and to this list: greetings. > > I need to get some points clear about precisely when objects are fully > instantiated in memory. It may be a simple matter of pointing me at some > documentation; I read pretty much anything I could find but there may a > problem of your jargon being different from mine:) > > The main data structure of my application is a directed graph of nodes; > each node has at least three slots which contain other nodes (e.g. > parent, right child, left child; the parent always exists, the child > slots may be None). I only want to instantiate that part of the graph > that I am working on. > > Q1. I assume that when an object is instantiated, its "sub" objects will > be in the form of some kind of proxy (perhaps that ghost I met in the > ZODB How document?). Is this assumption correct?
Yes. The ghost has not had its instance dictionary populated yet. Attempting to access any instance attribute will "unghostify" the object. > Q2. Given an object, designated by the variable a, in which of the > following statements does the child become instantiated (activated?) ? > child = a.leftchild > name = child.name The second (assuming that the nodes in your data structure derive from a "persistent" base class, such as Persistent, or one of the BTrees), > Q3. Actually, before the child is instantiated, I somehow would like to > query the object a, whether there is anything in the slot, i.e. whether > the content of the slot is not None. Of course, this query should not > trigger the instantiation. That should already be working, again assuming your objects derive from Persistent. > I had the application running in another OO language. An object would > first carry a proxy with the OID in a slot; it would get instantiated on > access. The ad-hoc database made use of the Reiser file system, which > allowed indexing serialized objects on their OID in a B tree. Tres. - -- =================================================================== Tres Seaver +1 540-429-0999 tsea...@palladion.com Palladion Software "Excellence by Design" http://palladion.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk065S4ACgkQ+gerLs4ltQ510wCfSujRaHMG7utqgsgRbEEHwmiI iFsAoKEv4K5tIPYR2su/o3aEUDyVfTta =2Jam -----END PGP SIGNATURE----- _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev
