Commit f0c45600 authored by Hanno Schlichting's avatar Hanno Schlichting

Added a chapter about using the IContainer API with object managers

parent 1d38e184
...@@ -247,3 +247,80 @@ no longer needs Acquisition wrapping for the Acquisition machinery to ...@@ -247,3 +247,80 @@ no longer needs Acquisition wrapping for the Acquisition machinery to
understand this. The next time you want to use a package or make your own code understand this. The next time you want to use a package or make your own code
more reusable outside of Zope2, this should be of tremendous help. more reusable outside of Zope2, this should be of tremendous help.
Object managers and IContainer
------------------------------
One of the fundamental parts of Zope2 is the object file system as implemented
in the `OFS` package. A central part of this package is an underlying class
called `ObjectManager`. It is a base class of the standard Folder used
for many container-ish classes inside Zope2.
The API to access objects in an object manager or to add objects to one has
been written many years ago. Since those times Python itself has gotten
standard ways to access objects in containers and work with them. Those Python
API's are most familiar to most developers working with Zope. The Zope
components libraries have formalized those API's into the general IContainer
interface in the zope.container package. In this version of Zope2 the standard
OFS ObjectManager fully implements this IContainer interface in addition to its
old API.
>>> from zope.container.interfaces import IContainer
>>> from OFS.ObjectManager import ObjectManager
>>> IContainer.implementedBy(ObjectManager)
True
You can now write any of your code in a way that no longer ties it to object
managers alone, but can support any class implementing IContainer instead. In
conjunction with the Acquisition changes above, this will increase your chances
of being able to reuse existing packages not specifically written for Zope2 in
a major way.
Here's an example of how you did work with object managers before::
>>> from OFS.Folder import Folder
>>> from OFS.SimpleItem import SimpleItem
>>> folder = Folder('folder')
>>> item1 = SimpleItem('item1')
>>> item2 = SimpleItem('item1')
>>> result = folder._setObject('item1', item1)
>>> result = folder._setObject('item2', item2)
>>> folder.objectIds()
['item1', 'item2']
>>> folder.objectValues()
[<SimpleItem at folder/>, <SimpleItem at folder/>]
>>> if folder.hasObject('item2')
... folder._delObject('item2')
Instead of this special API, you can now use::
>>> from OFS.Folder import Folder
>>> from OFS.SimpleItem import SimpleItem
>>> folder = Folder('folder')
>>> item1 = SimpleItem('item1')
>>> item2 = SimpleItem('item1')
>>> folder['item1'] = item1
>>> folder['item2'] = item2
>>> folder.keys()
['item1', 'item2']
>>> folder.values()
[<SimpleItem at folder/>, <SimpleItem at folder/>]
>>> folder.get('item1')
<SimpleItem at folder/>
>>> if 'item2' in folder:
... del folder['item2']
>>> folder.items()
[('item1', <SimpleItem at folder/>)]
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