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==========================================================
``zope.component.hooks``: The current component registry
==========================================================
.. currentmodule:: zope.component.hooks
There can be any number of component registries in an application. One of them
is the global component registry, and there is also the concept of a currently
used component registry. Component registries other than the global one are
associated with objects called sites. The :mod:`zope.component.hooks` module
provides an API to set and access the current site as well as manipulate the
adapter hook associated with it.
.. autofunction:: getSite
As long as we haven't set a site, none is being considered current:
.. doctest::
>>> from zope.component.hooks import getSite
>>> print(getSite())
None
We can also ask for the current component registry (aka site manager
historically); it will return the global one if no current site is set:
.. autofunction:: getSiteManager
.. doctest::
>>> from zope.component.hooks import getSiteManager
>>> getSiteManager()
<BaseGlobalComponents base>
Let's set a site now. A site has to be an object that provides the
``getSiteManager`` method, which is specified by
`zope.component.interfaces.IPossibleSite`:
.. autofunction:: setSite
.. doctest::
>>> from zope.interface.registry import Components
>>> class Site(object):
... def __init__(self):
... self.registry = Components('components')
... def getSiteManager(self):
... return self.registry
>>> from zope.component.hooks import setSite
>>> site1 = Site()
>>> setSite(site1)
After this, the newly set site is considered the currently active one:
.. doctest::
>>> getSite() is site1
True
>>> getSiteManager() is site1.registry
True
If we set another site, that one will be considered current:
.. doctest::
>>> site2 = Site()
>>> site2.registry is not site1.registry
True
>>> setSite(site2)
>>> getSite() is site2
True
>>> getSiteManager() is site2.registry
True
However, the default `zope.component.getSiteManager` function isn't
yet aware of this:
.. doctest::
>>> from zope.component import getSiteManager as global_getSiteManager
>>> global_getSiteManager()
<BaseGlobalComponents base>
To integrate that with the notion of the current site, we need to call ``setHooks``:
.. autofunction:: setHooks
.. doctest::
>>> from zope.component.hooks import setHooks
>>> setHooks()
>>> getSiteManager() is site2.registry
True
>>> global_getSiteManager() is site2.registry
True
This can be reversed using ``resetHooks``:
.. autofunction:: resetHooks
.. doctest::
>>> from zope.component.hooks import resetHooks
>>> resetHooks()
>>> global_getSiteManager()
<BaseGlobalComponents base>
Finally we can unset the site and the global component registry is used again:
.. doctest::
>>> setSite()
>>> print(getSite())
None
>>> getSiteManager()
<BaseGlobalComponents base>
Context manager
===============
There also is a context manager for setting the site, which is especially
useful when writing tests:
.. autofunction:: site
.. doctest::
>>> import zope.component.hooks
>>> print(getSite())
None
>>> with zope.component.hooks.site(site2):
... getSite() is site2
True
>>> print(getSite())
None
The site is properly restored even if the body of the with statement
raises an exception:
.. doctest::
>>> print(getSite())
None
>>> with zope.component.hooks.site(site2):
... getSite() is site2
... raise ValueError('An error in the body')
Traceback (most recent call last):
...
ValueError: An error in the body
>>> print(getSite())
None
|
