The current story for relating content in Plone, via Archetypes reference fields, is limited and known to have poor performance in some cases. This talk will focus on the integration of Zope 3 tools for handling relationships (intids, zc.relationship) in Zope 2 via plone.app.relations. In particular I will be comparing the merits of these tools against existing methods (Archetypes references, using a separate RDBMS for content relationships), discussing particular applications for which they may be useful, and some areas in which they fall short. The comparison to existing relationship modeling tools will cover performance, flexibility, and convenience. To illustrate the relative convenience, I will give a brief overview of the plone.app.relations API, from the lower level index and relationship container to the high level API for making queries and defining relationships. The discussion of applications will focus on a some real world uses. These include social networking, defining complex taxonomies, having content appear attached to multiple locations, and other things for which Plone typically would not be suitable (these tools are in use at http://www.thedailyreel.com). In particular, I'll discuss how the default relationship attributes and query methods from the API can be used to model each of these applications. Finally, I'll discuss the areas in which these tools may fall short in terms of performance and flexibility, and where an RDBMS or specialized catalog may be necessary.

1. Relationship Building
Defining and Querying Complex Relationships
Between Your Content
Alec P. Mitchell

2. Existing Tools
• Archetypes Reference Engine
• External SQL database
• zc.relationship + plone.relations
• ???

3. Benefits of AT
References
• Can relate any AT content to any other AT
content.
• There are nice widgets available to
manipulate relationships.
• Uses the familiar ZCatalog internally.
• Relationships can provide complex
behaviors.

4. Disadvantages of AT
References
• Requires mixin base classes. Essentially only
works with AT content.
• References are intrinsic to their source, and
generally defined as part of the content
schema.
• General purpose ZCatalog not entirely
optimized for relationship queries.
• API tends is somewhat inconsistent, and test
coverage is sub-optimal.

5. Benefits of an RDBMS-
based Solution
• Can support arbitrarily complex
relationships and queries.
• Can be performance tuned for specific use-
cases.
• Can be used to relate anything to anything
else.

6. Disadvantages of an
RDBMS-based Solution
• Entirely DIY
• Requires an external database
• Need to create some 1-to-1 mapping
between RDBMS keys and ZODB content.

7. What is zc.relationship
• A low-level ZODB index for querying
relationships
• Highly optimized for simple relationship
queries across large data-sets.
• Default configuration allows relationships
between arbitrary persistent objects.
• Index can be configured to index complex
relationships, which may include non-
ZODB objects.
• Provides transitive searches.

8. What is plone.relations
• A local utility built on zc.relationship, which
is applicable to a wide variety of relationship
models.
• A relationship class that models many-to-
many content relationships.
• Some optional aspects of the relationship
are also indexed:
• Relationship Type
• Relationship State
• Relationship Context

9. What is
plone.app.relations
• A content-centric API for defining and
querying relationships:
src = IRelationshipSource(ob)
src.createRelationship(target=ob2)
src.getTargets()
...
• A set of optional adapters and subscribers
• DCWorkflow for relationships
• “Holding” relationships
• Relationships which are copied when their
source is copied.

10. Relationship Sources
• IRelationshipSource
• Create (createRelationship), supports
multiple targets
• Query (getTargets, isLinked,
getRelationshipChains, getRelatonships)
• Modify (deleteRelationship,
getRelationships)

11. Relationship Targets
• IRelationshipTarget
• Same query methods and parameters as
IRelationshipSource + getSources
• ISymmetricRelation
• Query (isLinked, getRelationships,
getRelations)
• No transitivity, for now

12. Brief Code Example
>>> class IFriendship(IDCWorkflowableRelationship):
... “””A friendship”””
>>> source = IRelationshipSource(ob1)
>>> rel = source.createRelationship(ob2, relation=’friend’,
... interfaces=(IFriendship,))
>>> list(source.getRelationships(relation=’friend’))
[<Relationship ‘friend’ from (<Demo ob1>,) to (<Demo ob2>,)]
>>> list(rel.targets), list(rel.sources)
([<Demo ob2>], [<Demo ob1>])
>>> list(source.getTargets())
[<Demo ob2>]
>>> list(source.getRelationshipChains(target=ob2, maxDepth=5))
[(<Relationship ‘friend’ from (<Demo ob1>,) to (<Demo ob2>,)>,)]
>>> target = IRelationshipTarget(ob2)
>>> list(target.getSources(relation-’friend’))
[<Demo ob1>]
>>> target.isLinked(source=ob1)
True
>>> list(ISymmetricRelation(ob1).getRelations())
[<Demo ob2>]
>>> list(ISymmetricRelation(ob2).getRelations())
[<Demo ob1>]
>>> wf_rel = IDCWorkflowRelation(rel)
>>> wf_rel.workflow_id = ‘friend_workflow’
>>> wf.doAction(‘approve’)
>>> wf.state
‘approved’

13. What Can You Do With It?
• Model any non-container relationships you
might need.
• Social Networking (user user,
user group/workspace)
• User Favorites (user content)
• Placeless Content
• Taxonomies or Complex Vocabularies
• Related Content

14. What Have I Done With It?
• The Daily Reel (http://www.thedailyreel.com)
• Social network for online video creators
• Contacts (user relationships with approval)
• Crews (discussion groups)
• Videos which “belong” to crews and users
(placeless content)
• Favorite Content

15. Brief UI Demo

16. Shortcomings
• Relationships are inherently asymmetric,
with sources and targets on unequal footing.
• Relationships are unordered
• Requires persistent sources/targets/
contexts.
• Uses IntIds: fast but limits the number of
indexed objects to sys.maxint.
• No user-space tools/UI, yet.

17. When to Use
Something Else
• Efficient sorting on a large result set of
relationships.
• Complex queries. Currently there’s only
‘==’ (for source/target, state, context)
• Non-ZODB objects
• Don’t have time to make your own UI (stick
with AT for now)

18. The Future?
• Support for explicit ordering of relationships
• API providing permission based filtering
• UI (schema field, formlib widget)
• Move general code downstream into
zc.relationship

19. Thank You!
• Special thanks to
• Balazs Ree
• Gary Poster and Zope Corporation
• Whit Morriss
• Ramon Navarro Bosch
• The Daily Reel
• Vincenzo and the conference organizers
• And now we sprint!!