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"""
Part of the BlackStar filesystem (bsfs) module.
A copy of the license is provided with the project.
Author: Matthias Baumgartner, 2022
"""
# imports
import itertools
import typing
import rdflib
# bsfs imports
from bsfs import schema as bsc
from bsfs.query import ast
from bsfs.utils import errors, URI
# inner-module imports
from . import base
# exports
__all__: typing.Sequence[str] = (
'SparqlStore',
)
## code ##
class _Transaction():
"""Lightweight rdflib transactions for in-memory databases."""
# graph instance.
_graph: rdflib.Graph
# current log of added triples.
_added: typing.List[typing.Any]
# current log of removed triples.
_removed: typing.List[typing.Any]
def __init__(self, graph: rdflib.Graph):
self._graph = graph
# initialize internal structures
self.commit()
def commit(self):
"""Commit temporary changes."""
self._added = []
self._removed = []
def rollback(self):
"""Undo changes since the last commit."""
for triple in self._added:
self._graph.remove(triple)
for triple in self._removed:
self._graph.add(triple)
def add(self, triple: typing.Any):
"""Add a triple to the graph."""
if triple not in self._graph:
self._added.append(triple)
self._graph.add(triple)
def remove(self, triple: typing.Any):
"""Remove a triple from the graph."""
if triple in self._graph:
self._removed.append(triple)
self._graph.remove(triple)
class SparqlStore(base.TripleStoreBase):
"""Sparql-based triple store.
The sparql triple store uses a third-party backend
(currently rdflib) to store triples and manages them via
the Sparql query language.
"""
# The rdflib graph.
_graph: rdflib.Graph
# Current transaction.
_transaction: _Transaction
# The local schema.
_schema: bsc.Schema
def __init__(self):
super().__init__(None)
self._graph = rdflib.Graph()
self._transaction = _Transaction(self._graph)
self._schema = bsc.Schema.Empty()
# NOTE: mypy and pylint complain about the **kwargs not being listed (contrasting super)
# However, not having it here is clearer since it's explicit that there are no arguments.
@classmethod
def Open(cls) -> 'SparqlStore': # type: ignore [override] # pylint: disable=arguments-differ
return cls()
def commit(self):
self._transaction.commit()
def rollback(self):
self._transaction.rollback()
@property
def schema(self) -> bsc.Schema:
return self._schema
@schema.setter
def schema(self, schema: bsc.Schema):
# check args: Schema instanace
if not isinstance(schema, bsc.Schema):
raise TypeError(schema)
# check compatibility: No contradicting definitions
if not self.schema.consistent_with(schema):
raise errors.ConsistencyError(f'{schema} is inconsistent with {self.schema}')
# commit the current transaction
self.commit()
# adjust instances:
# nothing to do for added classes
# delete instances of removed classes
# get deleted classes
sub = self.schema - schema
# remove predicate instances
for pred in sub.predicates:
for src, trg in self._graph.subject_objects(rdflib.URIRef(pred.uri)):
self._transaction.remove((src, rdflib.URIRef(pred.uri), trg))
# remove node instances
for node in sub.nodes:
# iterate through node instances
for inst in self._graph.subjects(rdflib.RDF.type, rdflib.URIRef(node.uri)):
# remove triples where the instance is in the object position
for src, pred in self._graph.subject_predicates(inst):
self._transaction.remove((src, pred, inst))
# remove triples where the instance is in the subject position
for pred, trg in self._graph.predicate_objects(inst):
self._transaction.remove((inst, pred, trg))
# remove instance
self._transaction.remove((inst, rdflib.RDF.type, rdflib.URIRef(node.uri)))
# NOTE: Nothing to do for literals
# commit instance changes
self.commit()
# migrate schema
self._schema = schema
def get(self, node_type: bsc.Node, query: ast.filter.FilterExpression) -> typing.Iterator[URI]:
raise NotImplementedError()
def _has_type(self, subject: URI, node_type: bsc.Node) -> bool:
"""Return True if *subject* is a node of class *node_type* or a subclass thereof."""
if node_type not in self.schema.nodes():
raise errors.ConsistencyError(f'{node_type} is not defined in the schema')
subject_types = list(self._graph.objects(rdflib.URIRef(subject), rdflib.RDF.type))
if len(subject_types) == 0:
return False
if len(subject_types) == 1:
node = self.schema.node(URI(subject_types[0])) # type: ignore [arg-type] # URI is a subtype of str
if node == node_type:
return True
if node_type in node.parents():
return True
return False
raise errors.UnreachableError()
def exists(
self,
node_type: bsc.Node,
guids: typing.Iterable[URI],
) -> typing.Iterable[URI]:
return (subj for subj in guids if self._has_type(subj, node_type))
def create(
self,
node_type: bsc.Node,
guids: typing.Iterable[URI],
):
# check node_type
if node_type not in self.schema.nodes():
raise errors.ConsistencyError(f'{node_type} is not defined in the schema')
# check and create guids
for guid in guids:
subject = rdflib.URIRef(guid)
# check node existence
if (subject, rdflib.RDF.type, None) in self._graph:
# FIXME: node exists and may have a different type! ignore? raise? report?
continue
# add node
self._transaction.add((subject, rdflib.RDF.type, rdflib.URIRef(node_type.uri)))
def set(
self,
node_type: bsc.Node,
guids: typing.Iterable[URI],
predicate: bsc.Predicate,
values: typing.Iterable[typing.Any],
):
# check node_type
if node_type not in self.schema.nodes():
raise errors.ConsistencyError(f'{node_type} is not defined in the schema')
# check predicate
if predicate not in self.schema.predicates():
raise errors.ConsistencyError(f'{predicate} is not defined in the schema')
if not node_type <= predicate.domain:
raise errors.ConsistencyError(f'{node_type} must be a subclass of {predicate.domain}')
# NOTE: predicate.range is in the schema since predicate is in the schema.
# materialize values
values = set(values)
# check values
if len(values) == 0:
return
if predicate.unique and len(values) != 1:
raise ValueError(values)
if isinstance(predicate.range, bsc.Node):
values = set(values) # materialize to safeguard against iterators passed as argument
inconsistent = {val for val in values if not self._has_type(val, predicate.range)}
# catches nodes that don't exist and nodes that have an inconsistent type
if len(inconsistent) > 0:
raise errors.InstanceError(inconsistent)
# check guids
# FIXME: Fail or skip inexistent nodes?
guids = set(guids)
inconsistent = {guid for guid in guids if not self._has_type(guid, node_type)}
if len(inconsistent) > 0:
raise errors.InstanceError(inconsistent)
# add triples
pred = rdflib.URIRef(predicate.uri)
for guid, value in itertools.product(guids, values):
guid = rdflib.URIRef(guid)
# convert value
if isinstance(predicate.range, bsc.Literal):
value = rdflib.Literal(value, datatype=rdflib.URIRef(predicate.range.uri))
elif isinstance(predicate.range, bsc.Node):
value = rdflib.URIRef(value)
else:
raise errors.UnreachableError()
# clear triples for unique predicates
if predicate.unique:
for obj in self._graph.objects(guid, pred):
if obj != value:
self._transaction.remove((guid, pred, obj))
# add triple
self._transaction.add((guid, pred, value))
## EOF ##
|
