Hello, Is there any support within the framework for singletons? What I call singletons are objects that are instanciated and persisted only once, or at least should be. I find myself wanting to use these in several instances, notably when I create a class/object that acts as a gateway to an external system of some kind (like a web service). I create an object that provides a pythonic/zope-ish API to the rest of my objects/product code. I often like to use a persistent object (vs. a regular python module/package) in order to take advantage of things like caching, or giving options for configuration through the ZMI. Given this use case, it would be nice to have Zope provide a framework to support such things. It could enforce the uniqueness of the object in the entire system (absolutely no way to add more than one), and maybe provide a global mechanism to "find" the object not needing to know where in the tree it is, what it is called, or using the catalog (rather expensive?). Maybe something like a singleton flag and registry of somekind? I can kind of achieve this partly by doing things like "visible=0" is my CMF registration for example, forcing a specific id, enforcing rules in the manage_add type methods, and so on, but it all seems so kludgy. Not to mention I always have to know the name of the object, and possibly even the path, to get to it ... Redundant when there's always only one! I'm not looking for solutions, but ideas and thoughts ... Although if someone knows of ways to do this nicely, maybe with a third-party product for example, I'd love to hear about it! Thanks, Jean-François Doyon Internet Service Development and Systems Support / Spécialiste de dèveloppements internet et soutien technique Canada Centre for Remote Sensing/Centre Canadien de télédétection Natural Resources Canada/Ressources Naturelles Canada http://atlas.gc.ca Tel./Tél.: (613) 992-4902 Fax: (613) 947-2410
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Doyon, Jean-Francois wrote:
Hello,
Is there any support within the framework for singletons? What I call singletons are objects that are instanciated and persisted only once, or at least should be.
I find myself wanting to use these in several instances, notably when I create a class/object that acts as a gateway to an external system of some kind (like a web service).
I create an object that provides a pythonic/zope-ish API to the rest of my objects/product code. I often like to use a persistent object (vs. a regular python module/package) in order to take advantage of things like caching, or giving options for configuration through the ZMI.
Given this use case, it would be nice to have Zope provide a framework to support such things. It could enforce the uniqueness of the object in the entire system (absolutely no way to add more than one), and maybe provide a global mechanism to "find" the object not needing to know where in the tree it is, what it is called, or using the catalog (rather expensive?). Maybe something like a singleton flag and registry of somekind?
I can kind of achieve this partly by doing things like "visible=0" is my CMF registration for example, forcing a specific id, enforcing rules in the manage_add type methods, and so on, but it all seems so kludgy. Not to mention I always have to know the name of the object, and possibly even the path, to get to it ... Redundant when there's always only one!
I'm not looking for solutions, but ideas and thoughts ... Although if someone knows of ways to do this nicely, maybe with a third-party product for example, I'd love to hear about it!
CMF uses a base class called UniqueObject for its tools, which are normally "singletons": http://svn.zope.org/CMF/trunk/CMFCore/utils.py?rev=38507&view=auto In Zope3, one accomplishes your use case by registering a utility for the interface your singleton provides, without supplying a name. Tres. - -- =================================================================== Tres Seaver +1 202-558-7113 tseaver@palladion.com Palladion Software "Excellence by Design" http://palladion.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org iD8DBQFDOtqm+gerLs4ltQ4RAmdqAJ9qE9SCVEtrlM+GnemGtuOhTf8sXwCeKbDS Se0IViIBS9fP8oM9+RPrgxw= =7DOZ -----END PGP SIGNATURE-----
Doyon, Jean-Francois wrote at 2005-9-28 13:28 -0400:
Is there any support within the framework for singletons? What I call singletons are objects that are instanciated and persisted only once, or at least should be.
Such objects are often put into "Control_Panel". My "ZopeProfiler" is an example (among lots of others) <http://www.dieter.handshake.de/pyprojects/zope> -- Dieter
participants (3)
-
Dieter Maurer -
Doyon, Jean-Francois -
Tres Seaver