dolmen.relations 0.5

Dolmen relations

dolmen.relations is a thin layer above zc.relation, allowing a simple and straightforward implementation of standalone relationships between objects.

Getting started

In order to demonstrate the package’s features, we first set up a sane environment:

>>> from zope import component
>>> from zope.container.btree import BTreeContainer

>>> sm = component.getGlobalSiteManager()
>>> herd = getRootFolder()['herd'] = BTreeContainer()

Relations catalog

dolmen.relations provides a component called RelationCatalog that is in charge of registering the relations and finding them:

>>> from dolmen.relations import RelationCatalog, ICatalog
>>> sm.registerUtility(RelationCatalog(), ICatalog)

Relations container

To store the relations and trigger the needed events, dolmen.relations provides a btree container:

>>> from dolmen.relations import RelationsContainer
>>> relations = herd['_relations'] = RelationsContainer()

Content

Now, we need some content to get started. The tests module defines a Mammoth persistent object that we are going to use here:

>>> from dolmen.relations.tests import Mammoth

>>> manfred = herd['manfred'] = Mammoth()
>>> gunther = herd['gunther'] = Mammoth()

To be sure that our objects will be persisted and will be granted an int id, we commit:

>>> import transaction
>>> transaction.commit()

Relations

The relations proposed by dolmen.relations are of the “A to B” type. They allow you to link a source object with a target object. For tests purposes, we are going to create two Mammoth objects that are going to be used as source and target:

>>> from dolmen.relations import values, any
>>> from zope.intid.interfaces import IIntIds
>>> ids = component.getUtility(IIntIds)
>>> rcatalog = component.getUtility(ICatalog)

>>> gunther_id = ids.getId(gunther)
>>> manfred_id = ids.getId(manfred)

Simple relation

The first and simpliest relation type is the RelationValue. This relation is created with a source id and target id:

>>> relations["simple"] = values.RelationValue(gunther_id, manfred_id)

You can query the relations by giving the target and/or source id:

>>> found = list(rcatalog.findRelations({'target_id': manfred_id}))
>>> found
[<dolmen.relations.values.RelationValue object at ...>]

The relation has attributes dedicated to resolving the source or target:

>>> relation = found.pop()
>>> relation
<dolmen.relations.values.RelationValue object at ...>
>>> relation.source
<Mammoth gunther>
>>> relation.target
<Mammoth manfred>

Tagged relation

The second type of relation is the TaggedRelationValue. It allows us to add to the a source-target couple, a list of tags as a list of unicode strings:

>>> relations["tagged"] = values.TaggedRelationValue(
...           gunther_id, manfred_id, tags=[u'grok', u'dolmen'])

The relation can still be retrieved with a basic query:

>>> found = list(rcatalog.findRelations({'target_id': manfred_id}))
>>> found
[<dolmen.relations.values.RelationValue object at ...>, <dolmen.relations.values.TaggedRelationValue object at ...>]

It can also, now, be queried using a tag value:

>>> found = list(rcatalog.findRelations({'tag': any('grok')}))
>>> found
[<dolmen.relations.values.TaggedRelationValue object at ...>]

>>> found = list(rcatalog.findRelations({'tag': any('drupal')}))
>>> found
[]

Stateful relation

The third type of relation is the StatefulRelationValue. It adds, to the source-target couple, state information as a unicode string:

>>> relations["stateful"] = values.StatefulRelationValue(
...           gunther_id, manfred_id, state=u"private")

The relation can still be retrieved with a basic query:

>>> found = list(rcatalog.findRelations({'target_id': manfred_id}))
>>> found
[<dolmen.relations.values.RelationValue object at ...>, <dolmen.relations.values.TaggedRelationValue object at ...>, <dolmen.relations.values.StatefulRelationValue object at ...>]

It can also, now, be queried using the state string:

>>> found = list(rcatalog.findRelations({'state': any('private')}))
>>> found
[<dolmen.relations.values.StatefulRelationValue object at ...>]

>>> found = list(rcatalog.findRelations({'state': any('public')}))
>>> found
[]

Events

Whenever an object is deleted, the relations using it as source or target are deleted also:

>>> del herd['manfred']
>>> print list(herd['_relations'].keys())
[]
>>> found = list(rcatalog.findRelations({'target_id': manfred_id}))
>>> found
[]

Changelog

0.5 (2011-11-08)

• Catch an error from the intids when the ID have been removed. Return None in this case.

0.4 (2010-03-15)

• Add event when relation are deleted because a component of them has been deleted.

• Fix an error when you del container[reference_id] in a relation container of an inexisting relation (you should only get a KeyError).

0.3 (2010-03-10)

• Correct zip-safe flag on package.

• Fix potential NotYet errors by using register instead of getId IntIds method.

• Fix event when you don’t have a relation catalog available.

0.2 (2009-12-26)

• ZTK compatibility imports change.

0.1 (2009-10-20)

• Initial release