zope.principalannotation 3.6.0

PrincipalAnnotationUtility

The core of this package is the PrincipalAnnotationUtility class that stores annotations for principals and allows to get them easily.

It provides the IPrincipalAnnotationUtility interface:

>>> from zope.principalannotation.interfaces import IPrincipalAnnotationUtility
>>> from zope.principalannotation.utility import PrincipalAnnotationUtility
>>> from zope.interface.verify import verifyObject
>>> util = PrincipalAnnotationUtility()
>>> verifyObject(IPrincipalAnnotationUtility, util)
True

It provides three methods: getAnnotations, getAnnotationsById and hasAnnotations. Let’s create a testing principal and check out these methods:

>>> from zope.security.testing import Principal
>>> nadako = Principal('nadako')
>>> nadako.id
'nadako'

We can check if our principal has any annotations. Of course, it currently doesn’t have any:

>>> util.hasAnnotations(nadako)
False

We can get IAnnotations object using principal object itself:

>>> util.getAnnotations(nadako)
<zope.principalannotation.utility.Annotations object at 0x...>

Or using principal id:

>>> util.getAnnotationsById(nadako.id)
<zope.principalannotation.utility.Annotations object at 0x...>

Let’s get the IAnnotations object for our principal and play with it:

>>> annots = util.getAnnotations(nadako)

>>> from zope.interface.verify import verifyObject
>>> from zope.annotation.interfaces import IAnnotations
>>> verifyObject(IAnnotations, annots)
True

Let’s check the IAnnotation contract:

>>> bool(annots)
False

>>> annots['not.here']
Traceback (most recent call last):
...
KeyError: 'not.here'

>>> annots.get('not.here') is None
True

>>> annots.get('not.here', 42)
42

Note, that the IAnnotations object gets stored in the utility only when we set a key for it. This is a simple optimization that allows us not to store any data when all we do is simply checking for presense of annotation. The hasAnnotations method will return True after storing a key in the annotations:

>>> util.hasAnnotations(nadako)
False

>>> annots['its.here'] = 'some info'

>>> util.hasAnnotations(nadako)
True

We can also delete the existing key:

>>> del annots['its.here']

But we can’t delete the key that is (no more) existant:

>>> del annots['its.here']
Traceback (most recent call last):
...
KeyError: 'its.here'

Multiple annotation utilities

Imagine that your application has a root site object with its component registry (a.k.a. site manager) and that object has a sub-site object with its own component registry, and that component registry has the root’s component registry as its base.

In that case, we want the IAnnotations object to be available to retrieve annotations from higher-level utilities.

Let’s register our utility in the root site and create a sub-site with its own IPrincipalAnnotationUtility:

>>> root['util'] = util
>>> rootsm = root.getSiteManager()
>>> rootsm.registerUtility(util, IPrincipalAnnotationUtility)

>>> from zope.site.folder import Folder
>>> from zope.site.site import LocalSiteManager

>>> subsite = Folder()
>>> root['subsite'] = subsite
>>> subsm = LocalSiteManager(subsite)
>>> subsite.setSiteManager(subsm)

>>> util2 = PrincipalAnnotationUtility()
>>> subsite['util2'] = util2
>>> subsm.registerUtility(util2, IPrincipalAnnotationUtility)

Now, let’s create a key in the IAnnotations, provided by root utility:

>>> annots = util.getAnnotations(nadako)
>>> annots['root.number'] = 42

The subsite utility should get the annotation successfully:

>>> annots2 = util2.getAnnotations(nadako)
>>> bool(annots2)
True

>>> annots2['root.number']
42

If we have the key both in higher-level annotations and lower-level ones, the lower-level will have priority, but higher-level won’t be deleted or overriden:

>>> annots['another.number'] = 1
>>> annots2['another.number'] = 42

>>> annots['another.number']
1
>>> annots2['another.number']
42

If we’ll delete the key from lower-level, it will not be deleted from a higher level utility:

>>> del annots2['another.number']

>>> annots['another.number']
1
>>> annots2['another.number']
1

IPrincipal -> IAnnotations adapter

Of course, the most nice feature is that we can simply adapt our principal object to IAnnotations and get those annotations using standard way documented in zope.annotation package.

>>> annots = IAnnotations(nadako)
>>> annots
<zope.principalannotation.utility.Annotations object at 0x...>
>>> annots['root.number']
42

By default, the IAnnotation adapter uses the current site’s utility:

>>> IAnnotations(nadako) is util.getAnnotations(nadako)
True

>>> from zope.site.hooks import setSite
>>> setSite(subsite)

>>> IAnnotations(nadako) is util2.getAnnotations(nadako)
True

Howerver, we can use a binary multi-adapter to IAnnotations to specify some context object from which to get the annotations utility:

>>> from zope.component import getMultiAdapter

>>> annots = getMultiAdapter((nadako, root), IAnnotations)
>>> annots is util.getAnnotations(nadako)
True

>>> annots = getMultiAdapter((nadako, subsite), IAnnotations)
>>> annots is util2.getAnnotations(nadako)
True