Package: dolmen.relations
dolmen.relationsis a thin layer abovezc.relation, allowing a
simple and straightforward implementation of standalone relationships
between objects.Getting startedIn 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 catalogdolmen.relationsprovides a component calledRelationCatalogthat
is in charge of registering the relations and finding them:>>> from dolmen.relations import RelationCatalog, ICatalog
>>> sm.registerUtility(RelationCatalog(), ICatalog)Relations containerTo store the relations and trigger the needed events,dolmen.relationsprovides a btree container:>>> from dolmen.relations import RelationsContainer
>>> relations = herd['_relations'] = RelationsContainer()ContentNow, 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()RelationsThe relations proposed bydolmen.relationsare 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 relationThe first and simpliest relation type is theRelationValue. 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 relationThe second type of relation is theTaggedRelationValue. 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 relationThe third type of relation is theStatefulRelationValue. 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
[]EventsWhenever 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
[]Changelog0.5 (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