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@@ -2,12 +2,13 @@ import logging
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from abc import ABCMeta, abstractmethod
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-from flask import request
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-from rdflib import Graph
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+from rdflib import Dataset, Graph
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+from rdflib.query import ResultException
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from rdflib.resource import Resource
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from rdflib.term import URIRef
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+from rdflib.plugins.stores.sparqlstore import SPARQLUpdateStore
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-from lakesuperior.connectors.graph_store_connector import GraphStoreConnector
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+from lakesuperior.config_parser import config
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from lakesuperior.core.namespaces import ns_collection as nsc
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from lakesuperior.core.namespaces import ns_mgr as nsm
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@@ -29,7 +30,8 @@ def needs_rsrc(fn):
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class BaseRdfLayout(metaclass=ABCMeta):
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'''
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- This class exposes an interface to build graph store layouts.
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+ This class exposes an interface to build graph store layouts. It also
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+ provides the baics of the triplestore connection.
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Some store layouts are provided. New ones aimed at specific uses
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and optimizations of the repository may be developed by extending this
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@@ -60,23 +62,52 @@ class BaseRdfLayout(metaclass=ABCMeta):
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# N.B. This is Fuseki-specific.
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UNION_GRAPH_URI = URIRef('urn:x-arq:UnionGraph')
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+ _conf = config['application']['store']['ldp_rs']
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_logger = logging.getLogger(__module__)
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+ query_ep = _conf['webroot'] + _conf['query_ep']
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+ update_ep = _conf['webroot'] + _conf['update_ep']
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+
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## MAGIC METHODS ##
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def __init__(self, urn=None):
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- '''
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+ '''Initialize the graph store and a layout.
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+
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+ NOTE: `rdflib.Dataset` requires a RDF 1.1 compliant store with support
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+ for Graph Store HTTP protocol
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+ (https://www.w3.org/TR/sparql11-http-rdf-update/). Blazegraph supports
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+ this only in the (currently) unreleased 2.2 branch. It works with Jena,
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+ but other considerations would have to be made (e.g. Jena has no REST
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+ API for handling transactions).
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+
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+ In a more advanced development phase it could be possible to extend the
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+ SPARQLUpdateStore class to add non-standard interaction with specific
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+ SPARQL implementations in order to support ACID features provided
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+ by them; e.g. Blazegraph's RESTful transaction handling methods.
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+
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The layout can be initialized with a URN to make resource-centric
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operations simpler. However, for generic queries, urn can be None and
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- no `self.rsrc` is assigned. In this case, some methods will not be
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- available.
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+ no `self.rsrc` is assigned. In this case, some methods (the ones
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+ decorated by `@needs_rsrc`) will not be available.
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'''
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- self.conn = GraphStoreConnector()
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- self.ds = self.conn.ds
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+ self.ds = Dataset(self.store, default_union=True)
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+ self.ds.namespace_manager = nsm
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self._base_urn = urn
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+ @property
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+ def store(self):
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+ if not hasattr(self, '_store') or not self._store:
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+ self._store = SPARQLUpdateStore(
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+ queryEndpoint=self.query_ep,
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+ update_endpoint=self.update_ep,
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+ autocommit=False,
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+ dirty_reads=True)
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+
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+ return self._store
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+
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+
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@property
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def base_urn(self):
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'''
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@@ -114,15 +145,87 @@ class BaseRdfLayout(metaclass=ABCMeta):
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## PUBLIC METHODS ##
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+ def query(self, q, initBindings=None, nsc=nsc):
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+ '''
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+ Perform a SPARQL query on the triplestore.
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+
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+ This should provide non-abstract access, independent from the layout,
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+ therefore it should not be overridden by individual layouts.
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+
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+ @param q (string) SPARQL query.
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+
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+ @return rdflib.query.Result
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+ '''
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+ self._logger.debug('Sending SPARQL query: {}'.format(q))
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+ return self.ds.query(q, initBindings=initBindings, initNs=nsc)
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+
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+
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+ def update(self, q, initBindings=None, nsc=nsc):
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+ '''
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+ Perform a SPARQL update on the triplestore.
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+
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+ This should provide non-abstract access, independent from the layout,
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+ therefore it should not be overridden by individual layouts.
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+
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+ @param q (string) SPARQL-UPDATE query.
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+
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+ @return None
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+ '''
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+ self._logger.debug('Sending SPARQL update: {}'.format(q))
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+ return self.ds.query(q, initBindings=initBindings, initNs=nsc)
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+
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+
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+ def extract_rsrc(self, uri=None, graph=None, inbound=False):
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+ '''
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+ Extract an in-memory resource based on the copy of a graph on a subject.
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+
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+ @param uri (URIRef) Resource URI.
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+ @param graph (rdflib.term.URIRef | set(rdflib.graphURIRef)) The graph
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+ to extract from. This can be an URI for a single graph, or a list of
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+ graph URIs in which case an aggregate graph will be used.
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+ @param inbound (boolean) Whether to pull triples that have the resource
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+ URI as their object.
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+ '''
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+ uri = uri or self.base_urn
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+
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+ inbound_qry = '\n?s1 ?p1 {}'.format(self.base_urn.n3()) \
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+ if inbound else ''
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+
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+ q = '''
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+ CONSTRUCT {{
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+ {0} ?p ?o .{1}
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+ }} WHERE {{
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+ {0} ?p ?o .{1}
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+ FILTER (?p != premis:hasMessageDigest) .
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+ }}
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+ '''.format(uri.n3(), inbound_qry)
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+
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+ try:
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+ qres = self.query(q)
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+ except ResultException:
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+ # RDFlib bug? https://github.com/RDFLib/rdflib/issues/775
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+ g = Graph()
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+ else:
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+ g = qres.graph
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+
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+ return Resource(g, uri)
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+
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+
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+ ## INTERFACE METHODS ##
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+
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+ # Implementers of custom layouts should look into these methods to
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+ # implement.
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@abstractmethod
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@needs_rsrc
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- def out_graph(self, srv_mgd=True, inbound=False, embed_children=False):
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+ def out_rsrc(self, srv_mgd=True, inbound=False, embed_children=False):
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'''
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Graph obtained by querying the triplestore and adding any abstraction
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and filtering to make up a graph that can be used for read-only,
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API-facing results. Different layouts can implement this in very
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different ways, so it is an abstract method.
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+
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+ @return rdflib.resource.Resource
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'''
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pass
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Stefano Cossu