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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 abc
import typing
# inner-module imports
from bsfs.utils import URI, typename
import bsfs.schema as _schema
# exports
__all__: typing.Sequence[str] = (
'TripleStoreBase',
)
## code ##
class TripleStoreBase(abc.ABC):
"""
"""
# storage's URI. None implies a temporary location.
uri: typing.Optional[URI] = None
def __init__(self, uri: typing.Optional[URI] = None):
self.uri = uri
def __hash__(self) -> int:
uri = self.uri if self.uri is not None else id(self)
return hash((type(self), uri))
def __eq__(self, other) -> bool:
return isinstance(other, type(self)) \
and (( self.uri is not None \
and other.uri is not None \
and self.uri == other.uri ) \
or id(self) == id(other))
def __repr__(self) -> str:
return f'{typename(self)}(uri={self.uri})'
def __str__(self) -> str:
return f'{typename(self)}(uri={self.uri})'
def is_persistent(self) -> bool:
"""Return True if data is stored persistently."""
return self.uri is not None
@classmethod
@abc.abstractmethod
def Open(cls, **kwargs: typing.Any) -> 'TripleStoreBase': # pylint: disable=invalid-name # capitalized classmethod
"""Return a TripleStoreBase instance connected to *uri*."""
@abc.abstractmethod
def commit(self):
"""Commit the current transaction."""
@abc.abstractmethod
def rollback(self):
"""Undo changes since the last commit."""
@property
@abc.abstractmethod
def schema(self) -> _schema.Schema:
"""Return the store's local schema."""
@schema.setter
@abc.abstractmethod
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.
"""
@abc.abstractmethod
def exists(
self,
node_type: _schema.Node,
guids: typing.Iterable[URI],
):
"""
"""
@abc.abstractmethod
def create(
self,
node_type: _schema.Node,
guids: typing.Iterable[URI],
):
"""Create *guid* nodes with type *subject*."""
@abc.abstractmethod
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],
):
"""
"""
## EOF ##
|
