class Collection(dict):
"""A collection of handles.
Runtime representation of a collection's metadata. This is independent on
its physical representation and therefore uses any CollectionBackend to set
and/or retrieve the data.
A Collection is a dictionary, which's keys are the handles' names.
The values are Handle instances representing the metadata of these handles.
Additionally, a Collection has attributes to store data about the
collection itself:
Attributes of a collection:
name: str
store: IOMemory
meta: (named) Graph
conjunctive_graph: ConjunctiveGraph
To represent the metadata, Collections use a named graph per handle and an
additional named graph for collection level metadata. These graphs can be
queried via the collection's graph store and its corresponding conjunctive
graph.
"""
def __init__(self, src=None, name=None):
# TODO: What about the 'name' option? How to treat it, in case src
# provides a name already? For now use it only if src==None.
# type(src) == Collection => copy has its own 'name'?
# type(src) == Backend => rename in backend?
super(Collection, self).__init__()
if isinstance(src, Collection):
self._backend = None
# TODO: confirm this is correct behaviour and document it.
# Means, it is a pure runtime copy with no persistence and no
# update from backend.
self.update(src)
self.store = IOMemory()
for graph in src.store.contexts():
self.store.add_graph(graph)
if graph.identifier == Literal(src.name):
self.meta = graph
else:
self[str(graph.identifier)].meta = graph
self.conjunctive_graph = ConjunctiveGraph(store=self.store)
elif isinstance(src, CollectionBackend):
self._backend = src
self.store = None
# TODO: check for existence in reload() fails otherwise;
# If it turns out, that reload is never required outside of
# constructor, that check isn't needed!
self._reload()
elif src is None:
self._backend = None
self.store = IOMemory()
self.meta = Graph(store=self.store, identifier=Literal(name))
self.meta.add((DLNS.this, RDF.type, DLNS.Collection))
self.conjunctive_graph = ConjunctiveGraph(store=self.store)
else:
lgr.error("Unknown source for Collection(): %s" % type(src))
raise TypeError('Unknown source for Collection(): %s' % type(src))
@property
def name(self):
return str(self.meta.identifier)
@property
def url(self):
return self._backend.url
def __delitem__(self, key):
lgr.error("__delitem__ called.")
self_uri = self.meta.value(predicate=RDF.type, object=DLNS.Collection)
key_uri = self[key].meta.value(predicate=RDF.type, object=DLNS.Handle)
self.meta.remove((self_uri, DCTERMS.hasPart, key_uri))
self.store.remove_graph(self[key].name)
super(Collection, self).__delitem__(key)
def __setitem__(self, key, value):
if not isinstance(value, Handle):
raise TypeError("Can't add non-Handle object to a collection.")
super(Collection, self).__setitem__(key, value)
self_uri = self.meta.value(predicate=RDF.type, object=DLNS.Collection)
key_uri = self[key].meta.value(predicate=RDF.type, object=DLNS.Handle)
self.meta.add((self_uri, DCTERMS.hasPart, key_uri))
self.store.add_graph(self[key].meta)
def _reload(self):
# TODO: When do we need to reload outside of the constructor?
# May be override self.update() to additionally reload in case
# there is a backend.
if not self._backend:
# TODO: Error or warning? Depends on when we want to call this one.
# By now this should be an error (or even an exception).
lgr.error("Missing collection backend.")
return
# get the handles as instances of class Handle:
self.update(self._backend.get_handles())
# get collection level data:
collection_data = self._backend.get_collection()
# TODO: May be a backend can just pass a newly created store containing
# all the needed graphs. Would save us time and space for copy, but
# seems to be less flexible in case we find another way to store a set
# of named graphs and their conjunctive graph without the need of every
# collection to have its own store.
# Note: By using store.add() there seems to be no copy at all.
# Need to check in detail, how this is stored and whether it still
# works as intended.
# Note 2: Definitely not a copy and seems to work. Need more queries to
# check.
# cleanup old store, if exists
if self.store is not None:
self.store.gc()
del self.store
gc.collect()
# create new store for the graphs:
self.store = IOMemory()
# add collection's own graph:
self.store.add_graph(collection_data)
self.meta = collection_data
# add handles' graphs:
for handle in self:
self.store.add_graph(self[handle].meta)
# reference to the conjunctive graph to be queried:
self.conjunctive_graph = ConjunctiveGraph(store=self.store)
def query(self):
# Note: As long as we use general SPARQL-Queries, no method is needed,
# since this is a method of rdflib.Graph/rdflib.Store.
# But we will need some kind of prepared queries here.
# Also depends on the implementation of the 'ontology translation layer'
pass
def commit(self, msg="Collection updated."):
if not self._backend:
lgr.error("Missing collection backend.")
raise RuntimeError("Missing collection backend.")
self._backend.commit_collection(self, msg)
