References

Description

Inter-content references in Plone are done using the reference_catalog tool.

Introduction

Plone uses a persistent tool called reference_catalog to store (Archetypes) object references. It is used by the out-of-the-box "Related items" and you can use it in your own content types with ReferenceField.

reference_catalog references can be bidirectional.

The reference_catalog is a catalog just like the portal_catalog — it just uses different indexes and metadata.

The reference_catalog is defined in ReferenceEngine.py.

Using references

Here is an example how to use reference field to make programme -> researcher references, and how to do reverse look-ups for the relationship.

You use getReferences() and getBackReferences() methods to look up relationships.

Example:

from Products.CMFCore.utils import getToolByName
from Products.Archetypes.config import REFERENCE_CATALOG

def getResearcherProgrammes(researcher):
    """
    Find all Programmes which refer to this researcher.

    The Programme<->Researcher relationship is defined in Programme as::

      atapi.ReferenceField(
        name='researchers',
        widget=ReferenceBrowserWidget(
            label="Researchers",
            description="Researchers involved in this project",
            base_query={'object_provides': IResearcher.__identifier__ },
            allow_browse=0,
            show_results_without_query=1,
        ),
        multiValued=1,
        relationship="researchers_in_theme"
      ),

    @param researcher: Content item on the site
    """
    reference_catalog = getToolByName(researcher, REFERENCE_CATALOG)

    # relationship: field name used
    # Plone 4.1: objects=True argument to fetch full objects, not just
    # index brains
    references = reference_catalog.getBackReferences(
                        researcher,
                        relationship="researchers_in_theme")
    # Resolve Reference objects to full objects
    # Return a generator method which will yield all full objects
    return [ ref.getSourceObject() for ref in references ]