[rdf] add functions and tools to generate rdf graph

cubicweb/entities/adapters.py

@@ -23,7 +23,7 @@ from cubicweb import _
 from itertools import chain
 
 from logilab.mtconverter import TransformError
-from logilab.common.decorators import cached
+from logilab.common.decorators import cached, cachedproperty
 
 from cubicweb.entity import EntityAdapter
 from cubicweb import (Unauthorized, ValidationError, ViolatedConstraint,
@@ -32,6 +32,25 @@ from cubicweb.schema import constraint_name_for
 from cubicweb.predicates import is_instance, relation_possible, match_exception
 
 
+class EntityRDFAdapter(EntityAdapter):
+    """EntityRDFAdapter is to be specialized for each entity that wants to
+    be converted to RDF using the mechanism from cubicweb.rdf
+    """
+    __abstract__ = True
+
+    def __init__(self, _cw, **kwargs):
+        super().__init__(_cw, **kwargs)
+        self.entity.complete()
+
+    @cachedproperty
+    def uri(self):
+        return self.entity.cwuri
+
+    def triples(self):
+        """return sequence of 3-tuple of rdflib identifiers"""
+        raise NotImplementedError()
+
+
 class IDublinCoreAdapter(EntityAdapter):
     __regid__ = 'IDublinCore'
     __select__ = is_instance('Any')

cubicweb/rdf.py

+# -*- coding: utf-8 -*-
+# copyright 2019 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
+# contact http://www.logilab.fr -- mailto:contact@logilab.fr
+#
+# This program is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation, either version 2.1 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+from rdflib import Namespace, ConjunctiveGraph, plugin
+import rdflib_jsonld  # noqa
+
+plugin.register("jsonld", plugin.Serializer, "rdflib_jsonld.serializer", "JsonLDSerializer")
+
+RDF_MIMETYPE_TO_FORMAT = {
+    'application/rdf+xml': 'xml',
+    'text/turtle': 'turtle',
+    'text/n3': 'n3',
+    'application/n-quads': 'nquads',
+    'application/n-triples': 'nt',
+    'application/trig': 'trig',
+    'application/ld+json': 'json-ld',
+}
+
+namespaces = {
+    "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
+    "schema": "http://schema.org/",
+}
+
+NS_VARS = {ns: Namespace(uri) for ns, uri in namespaces.items()}
+
+
+# dict: name of CWEType -> list of regid of adapters derived from EntityRDFAdapter
+ETYPES_ADAPTERS = {
+}
+
+
+def conjunctive_graph():
+    """factory to build a ``ConjunctiveGraph`` and bind all namespaces
+    """
+    graph = ConjunctiveGraph()
+    for vocab, rdfns in NS_VARS.items():
+        graph.bind(vocab, rdfns)
+    return graph
+
+
+def iter_rdf_adapters(entity):
+    for adapter_id in ETYPES_ADAPTERS.get(entity.__regid__, ()):
+        adapter = entity.cw_adapt_to(adapter_id)
+        if adapter:
+            yield adapter
+
+
+def add_entity_to_graph(graph, entity):
+    for adapter in iter_rdf_adapters(entity):
+        for triple in adapter.triples():
+            graph.add(triple)

setup.py

@@ -73,6 +73,8 @@ setup(
         'pytz',
         'Markdown',
         'filelock',
+        'rdflib',
+        'rdflib-jsonld',
     ],
     entry_points={
         'console_scripts': [
@@ -102,10 +104,6 @@ setup(
             'pyramid_multiauth',
             'repoze.lru',
         ],
-        'rdf': [
-            'rdflib',
-            'rdflib-jsonld',
-        ],
         'sparql': [
             'fyzz >= 0.1.0',
         ],