first draft for a simple hooks based custom attribute storage,
with a BytesFileSystemStorage POC implementation.
Basically:
* a dictionary contains maps from which attribute of which entity types are
mapped to which custom storage
* hooks check for one of these entity type being added/modified/deleted
* read is based on the sql generator callback mecanism (used in vcsfile for
instance)
* all storages have the same basic interface (read, add, update, delete),
and should be pluggable in a transparent way (except at migration time
when one want to change from a storage to another)
* the sample BytesFileSystemStorage:
* may store Bytes attributes content of any entity type as file on the file system
* is based on one FSPATH rql/sql function and another _fsopen only available in sql
* has a dumb file name allocation algorithm
"""custom storages for the system source"""
from os import unlink, path as osp
from cubicweb.server.hook import Operation
ETYPE_ATTR_STORAGE = {}
def set_attribute_storage(repo, etype, attr, storage):
ETYPE_ATTR_STORAGE.setdefault(etype, {})[attr] = storage
repo.system_source.map_attribute(etype, attr, storage.sqlgen_callback)
class Storage(object):
"""abstract storage"""
def sqlgen_callback(self, generator, relation, linkedvar):
"""sql generator callback when some attribute with a custom storage is
accessed
"""
raise NotImplementedError()
def entity_added(self, entity, attr):
"""an entity using this storage for attr has been added"""
raise NotImplementedError()
def entity_updated(self, entity, attr):
"""an entity using this storage for attr has been updatded"""
raise NotImplementedError()
def entity_deleted(self, entity, attr):
"""an entity using this storage for attr has been deleted"""
raise NotImplementedError()
# TODO
# * make it configurable without code
# * better file path attribution
class BytesFileSystemStorage(Storage):
"""store Bytes attribute value on the file system"""
def __init__(self, defaultdir):
self.default_directory = defaultdir
def sqlgen_callback(self, generator, linkedvar, relation):
"""sql generator callback when some attribute with a custom storage is
accessed
"""
linkedvar.accept(generator)
return '_fsopen(%s.cw_%s)' % (
linkedvar._q_sql.split('.', 1)[0], # table name
relation.r_type) # attribute name
def entity_added(self, entity, attr):
"""an entity using this storage for attr has been added"""
if not entity._cw.transaction_data.get('fs_importing'):
try:
value = entity.pop(attr)
except KeyError:
pass
else:
fpath = self.new_fs_path(entity, attr)
# bytes storage used to store file's path
entity[attr]= Binary(fpath)
file(fpath, 'w').write(value.getvalue())
AddFileOp(entity._cw, filepath=fpath)
# else entity[attr] is expected to be an already existant file path
def entity_updated(self, entity, attr):
"""an entity using this storage for attr has been updatded"""
try:
value = entity.pop(attr)
except KeyError:
pass
else:
fpath = self.current_fs_path(entity, attr)
UpdateFileOp(entity._cw, filepath=fpath, filedata=value.getvalue())
def entity_deleted(self, entity, attr):
"""an entity using this storage for attr has been deleted"""
DeleteFileOp(entity._cw, filepath=self.current_fs_path(entity, attr))
def new_fs_path(self, entity, attr):
fpath = osp.join(self.default_directory, '%s_%s_%s' % (
self.default_directory, entity.eid, attr))
while osp.exists(fspath):
fspath = '_' + fspath
return fspath
def current_fs_path(self, entity, attr):
cu = entity._cw.system_sql('SELECT cw_%s.%s WHERE cw_eid=%s' %
(entity.__regid__, attr, entity.eid))
return cu.fetchone()[0]
class AddFileOp(Operation):
def rollback_event(self):
try:
unlink(self.filepath)
except:
pass
class DeleteFileOp(Operation):
def commit_event(self):
try:
unlink(self.filepath)
except:
pass
class UpdateFileOp(Operation):
def precommit_event(self):
try:
file(self.filepath, 'w').write(self.filedata)
except:
pass