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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.utils import URI
from bsfs.utils import errors
import bsfs.schema as _schema
# inner-module imports
from . import base
# exports
__all__: typing.Sequence[str] = (
'SparqlStore',
)
## code ##
class Transaction():
"""Lightweight rdflib transactions for in-memory databases."""
def __init__(self, graph):
self._graph = graph
self.commit() # initialize
def commit(self):
self._added = []
self._removed = []
def rollback(self):
for triple in self._added:
self._graph.remove(triple)
for triple in self._removed:
self._graph.add(triple)
def add(self, triple):
if triple not in self._graph:
self._added.append(triple)
self._graph.add(triple)
def remove(self, triple):
if triple in self._graph:
self._removed.append(triple)
self._graph.remove(triple)
class SparqlStore(base.TripleStoreBase):
"""
"""
def __init__(self, uri: typing.Optional[URI] = None):
super().__init__(uri)
self.graph = rdflib.Graph()
self.transaction = Transaction(self.graph)
self.__schema = _schema.Schema.Empty()
@classmethod
def Open(
cls,
uri: str,
**kwargs: typing.Any,
) -> 'SparqlStore':
return cls(None)
def commit(self):
self.transaction.commit()
def rollback(self):
self.transaction.rollback()
@property
def schema(self) -> _schema.Schema:
"""Return the current schema."""
return self.__schema
@schema.setter
def schema(self, schema: _schema.Schema):
"""Migrate to new schema by adding or removing class definitions.
Commits before and after the migration.
Instances of removed classes will be deleted irreversably.
Note that modifying an existing class is not directly supported.
Also, it is generally discouraged, since changing definitions may
lead to inconsistencies across multiple clients in a distributed
setting. Instead, consider introducing a new class under its own
uri. Such a migration would look as follows:
1. Add new class definitions.
2. Create instances of the new classes and copy relevant data.
3. Remove the old definitions.
To modify a class, i.e., re-use a previous uri with a new
class definition, you would have to migrate via temporary
class definitions, and thus repeat the above procedure two times.
"""
# check args: Schema instanace
if not isinstance(schema, _schema.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 _has_type(self, subject: URI, node_type: _schema.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
elif len(subject_types) == 1:
node = self.schema.node(URI(subject_types[0]))
if node == node_type:
return True
elif node_type in node.parents():
return True
else:
return False
else:
raise errors.UnreachableError()
def exists(
self,
node_type: _schema.Node,
guids: typing.Iterable[URI],
):
"""
"""
return {subj for subj in guids if self._has_type(subj, node_type)}
def create(
self,
node_type: _schema.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:
guid = rdflib.URIRef(guid)
# check node existence
if (guid, 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((guid, rdflib.RDF.type, rdflib.URIRef(node_type.uri)))
def set(
self,
node_type: _schema.Node, # FIXME: is the node_type even needed? Couldn't I infer from the predicate?
guids: typing.Iterable[URI],
predicate: _schema.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.
# check values
if len(values) == 0:
return
if predicate.unique and len(values) != 1:
raise ValueError(values)
if isinstance(predicate.range, _schema.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, _schema.Literal):
value = rdflib.Literal(value, datatype=rdflib.URIRef(predicate.range.uri))
elif isinstance(predicate.range, _schema.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 ##
|
