Sites and Local Site Managers

This chapter is an introduction of the location-based component architecture. This code uses the registration framework introduced in registration.txt and local adapter registries described in adapterregistry.txt.

Creating and Accessing Sites

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

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

has the potential to become a site

>>> from zope.app.component import interfaces
>>> interfaces.IPossibleSite.providedBy(myfolder)
True

but is not yet one:

>>> interfaces.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.app.component import site
>>> class MyContentComponent(site.SiteManagerContainer):
...     pass
>>> myContent = MyContentComponent()
>>> interfaces.IPossibleSite.providedBy(myContent)
True
>>> interfaces.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)
>>> interfaces.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.app.component.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

Also, 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.app.component 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.app.component.site.SiteManagementFolder'>

You can easily create a new site management folder:

>>> sm['mySMF'] = site.SiteManagementFolder()
>>> sm['mySMF'].__class__
<class 'zope.app.component.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.app.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.app import zapi
>>> gsm = zapi.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 ZAPI's getSiteManager() method to get the nearest site manager:

>>> zapi.getSiteManager() is sm
True

This also means that you can simply use ZAPI to look up your utility

>>> zapi.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.app import container
>>> gsm.registerHandler(
...    site.changeSiteConfigurationAfterMove,
...    (interfaces.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
()

Finally, 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.app.component.tests'].IMyUtility = IMyUtility
>>> IMyUtility.__module__ = 'zope.app.component.tests'
>>> sys.modules['zope.app.component.tests'].MyUtility = MyUtility
>>> MyUtility.__module__ = 'zope.app.component.tests'
>>> from zope.location.pickling import locationCopy
>>> myfolder['myfolder11'] = locationCopy(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