zope.site 3.6.1

Local registries for zope component architecture

This package adds support for persistent local component registries for the zope component architecture.

Detailed Documentation

Zope 3’s Local Component Architecture

This package provides a local and persistent site manager implementation, so that one can register local utilities and adapters. It uses local adapter registries for its adapter and utility registry. The module also provides some facilities to organize the local software and ensures the correct behavior inside the ZODB.

Local Component Architecture API

While the component architecture API provided by zope.component is sufficient most of the time, there are a couple of functions that are useful in the context of multiple sites and base component registries.

It is common for a utility to delegate its answer to a utility providing the same interface in one of the component registry’s bases. Let’s first create a global utility:

>>> import zope.interface
>>> class IMyUtility(zope.interface.Interface):
...     pass

>>> class MyUtility(object):
...     zope.interface.implements(IMyUtility)
...     def __init__(self, id):
...         self.id = id
...     def __repr__(self):
...         return "%s('%s')" % (self.__class__.__name__, self.id)

>>> gutil = MyUtility('global')
>>> from zope.component import getGlobalSiteManager
>>> gsm = getGlobalSiteManager()
>>> gsm.registerUtility(gutil, IMyUtility, 'myutil')

We create a simple folder hierarchy we can place our utilities in:

>>> from zope.site.folder import Folder, rootFolder
>>> root = rootFolder()
>>> root[u'folder1'] = Folder()
>>> root[u'folder1'][u'folder1_1'] = Folder()

We set up site managers in the folders:

>>> from zope.site import testing
>>> root_sm = testing.createSiteManager(root)
>>> folder1_sm = testing.createSiteManager(root['folder1'])
>>> folder1_1_sm = testing.createSiteManager(root['folder1']['folder1_1'])

Now we create two utilities and insert them in our folder hierarchy:

>>> util1 = testing.addUtility(folder1_sm, 'myutil', IMyUtility,
...                            MyUtility('one'))
>>> util1_1 = testing.addUtility(folder1_1_sm, 'myutil', IMyUtility,
...                              MyUtility('one-one'))

Now, if we ask util1_1 for its next available utility we get the one utility:

>>> from zope import site
>>> site.getNextUtility(util1_1, IMyUtility, 'myutil')
MyUtility('one')

Next we ask util1 for its next utility and we should get the global version:

>>> site.getNextUtility(util1, IMyUtility, 'myutil')
MyUtility('global')

However, if we ask the global utility for the next one, an error is raised

>>> site.getNextUtility(gutil, IMyUtility,
...                     'myutil') #doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
ComponentLookupError:
No more utilities for <InterfaceClass __builtin__.IMyUtility>,
'myutil' have been found.

You can also use queryNextUtility and specify a default:

>>> site.queryNextUtility(gutil, IMyUtility, 'myutil', 'default')
'default'

Let’s now ensure that the function also works with multiple registries. First we create another base registry:

>>> from zope.component import registry
>>> myregistry = registry.Components()

We now set up another utility into that registry:

>>> custom_util = MyUtility('my_custom_util')
>>> myregistry.registerUtility(custom_util, IMyUtility, 'my_custom_util')

We add it as a base to the local site manager:

>>> folder1_sm.__bases__ = (myregistry,) + folder1_sm.__bases__

Both the myregistry and global utilities should be available:

>>> site.queryNextUtility(folder1_sm, IMyUtility, 'my_custom_util')
MyUtility('my_custom_util')
>>> site.queryNextUtility(folder1_sm, IMyUtility, 'myutil')
MyUtility('global')

Sites and Local Site Managers

This is an introduction of location-based component architecture.

Creating and Accessing Sites

Sites are used to provide custom component setups for parts of your application or web site. Every folder:

>>> from zope.site import folder
>>> myfolder = folder.rootFolder()

has the potential to become a site:

>>> from zope.location.interfaces import ISite, IPossibleSite
>>> IPossibleSite.providedBy(myfolder)
True

but is not yet one:

>>> ISite.providedBy(myfolder)
False

If you would like your custom content component to be able to become a site, you can use the SiteManagerContainer mix-in class:

>>> from zope import site
>>> class MyContentComponent(site.SiteManagerContainer):
...     pass

>>> myContent = MyContentComponent()
>>> IPossibleSite.providedBy(myContent)
True
>>> ISite.providedBy(myContent)
False

To convert a possible site to a real site, we have to provide a site manager:

>>> sm = site.LocalSiteManager(myfolder)
>>> myfolder.setSiteManager(sm)
>>> ISite.providedBy(myfolder)
True
>>> myfolder.getSiteManager() is sm
True

Note that an event is generated when a local site manager is created:

>>> from zope.component.eventtesting import getEvents
>>> from zope.site.interfaces import INewLocalSite
>>> [event] = getEvents(INewLocalSite)
>>> event.manager is sm
True

If one tries to set a bogus site manager, a ValueError will be raised:

>>> myfolder2 = folder.Folder()
>>> myfolder2.setSiteManager(object)
Traceback (most recent call last):
...
ValueError: setSiteManager requires an IComponentLookup

If the possible site has been changed to a site already, a TypeError is raised when one attempts to add a new site manager:

>>> myfolder.setSiteManager(site.LocalSiteManager(myfolder))
Traceback (most recent call last):
...
TypeError: Already a site

There is also an adapter you can use to get the next site manager from any location:

>>> myfolder['mysubfolder'] = folder.Folder()
>>> import zope.component
>>> zope.component.interfaces.IComponentLookup(myfolder['mysubfolder']) is sm
True

If the location passed is a site, the site manager of that site is returned:

>>> zope.component.interfaces.IComponentLookup(myfolder) is sm
True

During traversal,

>>> from zope.app import publication
>>> request = object()
>>> ev = publication.interfaces.BeforeTraverseEvent(myfolder, request)
>>> site.threadSiteSubscriber(myfolder, ev)

the nearest site is also recorded in a thread-global variable:

>>> from zope.site import hooks
>>> hooks.getSite() is myfolder
True

After a request is completed, the site setting is cleared again:

>>> ev = publication.interfaces.EndRequestEvent(myfolder, request)
>>> site.clearThreadSiteSubscriber(ev)
>>> hooks.getSite() is None
True

Using the Site Manager

A site manager contains several site management folders, which are used to logically organize the software. When a site manager is initialized, a default site management folder is created:

>>> sm = myfolder.getSiteManager()
>>> default = sm['default']
>>> default.__class__
<class 'zope.site.site.SiteManagementFolder'>

However, you can tell not to create the default site manager folder on LocalSiteManager creation:

>>> nodefault = site.LocalSiteManager(myfolder, default_folder=False)
>>> 'default' in nodefault
False

You can easily create a new site management folder:

>>> sm['mySMF'] = site.SiteManagementFolder()
>>> sm['mySMF'].__class__
<class 'zope.site.site.SiteManagementFolder'>

Once you have your site management folder – let’s use the default one – we can register some components. Let’s start with a utility:

>>> import zope.interface
>>> class IMyUtility(zope.interface.Interface):
...     pass

>>> import persistent
>>> from zope.container.contained import Contained
>>> class MyUtility(persistent.Persistent, Contained):
...     zope.interface.implements(IMyUtility)
...     def __init__(self, title):
...         self.title = title
...     def __repr__(self):
...         return "%s('%s')" %(self.__class__.__name__, self.title)

Now we can create an instance of our utility and put it in the site management folder and register it:

>>> myutil = MyUtility('My custom utility')
>>> default['myutil'] = myutil
>>> sm.registerUtility(myutil, IMyUtility, 'u1')

Now we can ask the site manager for the utility:

>>> sm.queryUtility(IMyUtility, 'u1')
MyUtility('My custom utility')

Of course, the local site manager has also access to the global component registrations:

>>> gutil = MyUtility('Global Utility')
>>> from zope.component import getGlobalSiteManager
>>> gsm = getGlobalSiteManager()
>>> gsm.registerUtility(gutil, IMyUtility, 'gutil')

>>> sm.queryUtility(IMyUtility, 'gutil')
MyUtility('Global Utility')

Next let’s see whether we can also successfully register an adapter as well. Here the adapter will provide the size of a file:

>>> class IFile(zope.interface.Interface):
...     pass

>>> class ISized(zope.interface.Interface):
...     pass

>>> class File(object):
...     zope.interface.implements(IFile)

>>> class FileSize(object):
...     zope.interface.implements(ISized)
...     def __init__(self, context):
...         self.context = context

Now that we have the adapter we need to register it:

>>> sm.registerAdapter(FileSize, [IFile])

Finally, we can get the adapter for a file:

>>> file = File()
>>> size = sm.queryAdapter(file, ISized, name='')
>>> size.__class__
<class 'FileSize'>
>>> size.context is file
True

By the way, once you set a site

>>> hooks.setSite(myfolder)

you can simply use the zope.component’s getSiteManager() method to get the nearest site manager:

>>> from zope.component import getSiteManager
>>> getSiteManager() is sm
True

This also means that you can simply use zope.component to look up your utility

>>> from zope.component import getUtility
>>> getUtility(IMyUtility, 'gutil')
MyUtility('Global Utility')

or the adapter via the interface’s __call__ method:

>>> size = ISized(file)
>>> size.__class__
<class 'FileSize'>
>>> size.context is file
True

Multiple Sites

Until now we have only dealt with one local and the global site. But things really become interesting, once we have multiple sites. We can override other local configuration.

Let’s now create a new folder called folder11, add it to myfolder and make it a site:

>>> myfolder11 = folder.Folder()
>>> myfolder['myfolder11'] = myfolder11
>>> myfolder11.setSiteManager(site.LocalSiteManager(myfolder11))
>>> sm11 = myfolder11.getSiteManager()

If we ask the second site manager for its next, we get

>>> sm11.__bases__ == (sm, )
True

and the first site manager should have the folling sub manager:

>>> sm.subs == (sm11,)
True

If we now register a second utility with the same name and interface with the new site manager folder,

>>> default11 = sm11['default']
>>> myutil11 = MyUtility('Utility, uno & uno')
>>> default11['myutil'] = myutil11

>>> sm11.registerUtility(myutil11, IMyUtility, 'u1')

then it will will be available in the second site manager

>>> sm11.queryUtility(IMyUtility, 'u1')
MyUtility('Utility, uno & uno')

but not in the first one:

>>> sm.queryUtility(IMyUtility, 'u1')
MyUtility('My custom utility')

It is also interesting to look at the use cases of moving and copying a site. To do that we create a second root folder and make it a site, so that site hierarchy is as follows:

         _____ global site _____
        /                       \
    myfolder1                myfolder2
        |
    myfolder11


>>> myfolder2 = folder.rootFolder()
>>> myfolder2.setSiteManager(site.LocalSiteManager(myfolder2))

Before we can move or copy sites, we need to register two event subscribers that manage the wiring of site managers after moving or copying:

>>> from zope import container
>>> gsm.registerHandler(
...    site.changeSiteConfigurationAfterMove,
...    (ISite, container.interfaces.IObjectMovedEvent),
...    )

We only have to register one event listener, since the copy action causes an IObjectAddedEvent to be created, which is just a special type of IObjectMovedEvent.

First, make sure that everything is setup correctly in the first place:

>>> myfolder11.getSiteManager().__bases__ == (myfolder.getSiteManager(), )
True
>>> myfolder.getSiteManager().subs[0] is myfolder11.getSiteManager()
True
>>> myfolder2.getSiteManager().subs
()

Let’s now move myfolder11 from myfolder to myfolder2:

>>> myfolder2['myfolder21'] = myfolder11
>>> del myfolder['myfolder11']

Now the next site manager for myfolder11’s site manager should have changed:

>>> myfolder21 = myfolder11
>>> myfolder21.getSiteManager().__bases__ == (myfolder2.getSiteManager(), )
True
>>> myfolder2.getSiteManager().subs[0] is myfolder21.getSiteManager()
True
>>> myfolder.getSiteManager().subs
()

Now, we make a copy of myfolder21 and add it as myfolder11 to myfolder:

# Make sure that our interfaces and classes are picklable.

>>> import sys
>>> sys.modules['zope.site.tests'].IMyUtility = IMyUtility
>>> IMyUtility.__module__ = 'zope.site.tests'
>>> sys.modules['zope.site.tests'].MyUtility = MyUtility
>>> MyUtility.__module__ = 'zope.site.tests'

>>> from zope.copy import copy
>>> myfolder['myfolder11'] = copy(myfolder2['myfolder21'])

>>> myfolder11 = myfolder['myfolder11']
>>> myfolder11.getSiteManager().__bases__ == (myfolder.getSiteManager(), )
True
>>> myfolder.getSiteManager().subs[0] is myfolder11.getSiteManager()
True
>>> myfolder2.getSiteManager().subs[0] is myfolder21.getSiteManager()
True

Finally, let’s check that everything works fine when our folder is moved to the folder that doesn’t contain any site manager. Our folder’s sitemanager’s bases should be set to global site manager.

>>> myfolder11.getSiteManager().__bases__ == (myfolder.getSiteManager(), )
True

>>> nosm = folder.Folder()
>>> nosm['root'] = myfolder11
>>> myfolder11.getSiteManager().__bases__ == (gsm, )
True

CHANGES

3.6.1 (2009-02-28)

• Import symbols moved from zope.traversing to zope.location from the new location.

• Don’t fail when changing component registry bases while moving ISite object to non-ISite object.

• Allow specify whether to create ‘default’ SiteManagementFolder on initializing LocalSiteManager. Use the default_folder argument.

• Add a containment constraint to the SiteManagementFolder that makes it only available to be contained in ILocalSiteManagers and other ISiteManagementFolders.

• Change package’s mailing list address to zope-dev at zope.org, as zope3-dev at zope.org is now retired.

• Remove old unused code. Update package description.

3.6.0 (2009-01-31)

• Use zope.container instead of zope.app.container.

3.5.1 (2009-01-27)

• Extracted from zope.app.component (trunk, 3.5.1 under development) as part of an effort to clean up dependencies between Zope packages.