Using zope.dublincore

Dublin Core Properties

A dublin core property allows us to use properties from dublin core by simply defining a property as DCProperty.

>>> from zope.dublincore import property

>>> from zope.interface import implementer
>>> from zope.annotation.interfaces import IAttributeAnnotatable
>>> @implementer(IAttributeAnnotatable)
... class DC(object):
...     title   = property.DCProperty('title')
...     author  = property.DCProperty('creators')
...     authors = property.DCListProperty('creators')
>>> obj = DC()
>>> obj.title = u'My title'
>>> obj.title
u'My title'

Let’s see if the title is really stored in dublin core:

>>> from zope.dublincore.interfaces import IZopeDublinCore
>>> IZopeDublinCore(obj).title
u'My title'

Even if a dublin core property is a list property we can set and get the property as scalar type:

>>> obj.author = u'me'
>>> obj.author
u'me'

DCListProperty acts on the list:

>>> obj.authors
(u'me',)
>>> obj.authors = [u'I', u'others']
>>> obj.authors
(u'I', u'others')
>>> obj.author
u'I'

Dublin Core metadata as content data

Sometimes we want to include data in content objects which mirrors one or more Dublin Core fields. In these cases, we want the Dublin Core structures to use the data in the content object rather than keeping a separate value in the annotations typically used. What fields we want to do this with can vary, however, and we may not want the Dublin Core APIs to constrain our choices of field names for our content objects.

To deal with this, we can use speciallized adapter implementations tailored to specific content objects. To make this a bit easier, there is a factory for such adapters.

Let’s take a look at the simplest case of this to start with. We have some content object with a title attribute that should mirror the Dublin Core title field:

>>> @implementer(IAttributeAnnotatable)
... class Content(object):
...     title = u""
...     description = u""

To avoid having a discrepency between the title attribute of our content object and the equivalent Dublin Core field, we can provide a specific adapter for our object:

>>> from zope.dublincore import annotatableadapter

>>> factory = annotatableadapter.partialAnnotatableAdapterFactory(
...     ["title"])

This creates an adapter factory that maps the Dublin Core title field to the title attribute on instances of our Content class. Multiple mappings may be specified by naming the additional fields in the sequence passed to partialAnnotatableAdapterFactory(). (We’ll see later how to use different attribute names for Dublin Core fields.)

Let’s see what happens when we use the adapter.

When using the adapter to retrieve a field set to use the content object, the value stored on the content object is used:

>>> content = Content()
>>> adapter = factory(content)

>>> adapter.title
u''

>>> content.title = u'New Title'
>>> adapter.title
u'New Title'

If we set the relevant Dublin Core field using the adapter, the content object is updated:

>>> adapter.title = u'Adapted Title'
>>> content.title
u'Adapted Title'

Dublin Core fields which are not specifically mapped to the content object do not affect the content object:

>>> adapter.description = u"Some long description."
>>> content.description
u''
>>> adapter.description
u'Some long description.'

Using arbitrary field names

We’ve seen the simple approach, allowing a Dublin Core field to be stored on the content object using an attribute of the same name as the DC field. However, we may want to use a different name for some reason. The partialAnnotatableAdapterFactory() supports this as well.

If we call partialAnnotatableAdapterFactory() with a mapping instead of a sequence, the mapping is used to map Dublin Core field names to attribute names on the content object.

Let’s look at an example where we want the abstract attribute on the content object to be used for the description Dublin Core field:

>>> @implementer(IAttributeAnnotatable)
... class Content(object):
...     abstract = u""

We can create the adapter factory by passing a mapping to partialAnnotatableAdapterFactory():

>>> factory = annotatableadapter.partialAnnotatableAdapterFactory(
...     {"description": "abstract"})

We can check the effects of the adapter as before:

>>> content = Content()
>>> adapter = factory(content)

>>> adapter.description
u''

>>> content.abstract = u"What it's about."
>>> adapter.description
u"What it's about."

>>> adapter.description = u'Change of plans.'
>>> content.abstract
u'Change of plans.'

Limitations

The current implementation has a number of limitations to be aware of; hopefully these can be removed in the future.

  • Only simple string properties, like title, are supported. This is largely because other field types have not been given sufficient thought. Attempting to use this for other fields will cause a ValueError to be raised by partialAnnotatableAdapterFactory().
  • The CMF-like APIs are not supported in the generated adapters. It is not clear that these APIs are used, but content object implementations should be aware of this limitation.

Time annotators

Time annotators store the creation resp. last modification time of an object. We will use a simple Content class as our example.

>>> class Content(object):
...     created = None
...     modified = None

The annotations are stored on the IZopeDublinCore adapter. This dummy adapter reads and writes from/to the context object.

>>> from zope.component import provideAdapter
>>> from zope.dublincore.interfaces import IZopeDublinCore
>>> class DummyDublinCore(object):
...     def __init__(self, context):
...         self.__dict__['context'] = context
...
...     def __getattr__(self, name):
...         return getattr(self.context, name)
...
...     def __setattr__(self, name, value):
...         setattr(self.context, name, value)

>>> provideAdapter(DummyDublinCore, (Content,), IZopeDublinCore)

Created annotator

The created annotator sets creation and modification time to current time.

>>> content = Content()

It is registered for the ObjectCreatedEvent:

>>> from zope.dublincore import timeannotators
>>> timeannotators._NOW = 'NOW'
>>> from zope.component import provideHandler
>>> from zope.dublincore.timeannotators import CreatedAnnotator
>>> from zope.lifecycleevent.interfaces import IObjectCreatedEvent
>>> provideHandler(CreatedAnnotator, (IObjectCreatedEvent,))

>>> from zope.event import notify
>>> from zope.lifecycleevent import ObjectCreatedEvent
>>> notify(ObjectCreatedEvent(content))

Both created and modified get set:

>>> content.created
'NOW'
>>> content.modified
'NOW'

The created annotator can also be registered for (object, event):

>>> from zope.component import subscribers
>>> provideHandler(CreatedAnnotator, (None, IObjectCreatedEvent,))
>>> content = Content()
>>> ignored = subscribers((content, ObjectCreatedEvent(content)), None)

Both created and modified get set this way, too:

>>> content.created
'NOW'
>>> content.modified
'NOW'

Modified annotator

The modified annotator only sets the modification time to current time.

>>> content = Content()

It is registered for the ObjectModifiedEvent:

>>> from zope.dublincore.timeannotators import ModifiedAnnotator
>>> from zope.lifecycleevent.interfaces import IObjectModifiedEvent
>>> provideHandler(ModifiedAnnotator, (IObjectModifiedEvent,))

>>> from zope.lifecycleevent import ObjectModifiedEvent
>>> notify(ObjectModifiedEvent(content))

Only modified gets set:

>>> print(content.created)
None
>>> content.modified
'NOW'

The modified annotator can also be registered for (object, event):

>>> provideHandler(ModifiedAnnotator, (None, IObjectModifiedEvent,))
>>> content = Content()
>>> ignored = subscribers((content, ObjectModifiedEvent(content)), None)

modified gets set, this way, too:

>>> print(content.created)
None
>>> content.modified
'NOW'