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
/* -*- sql -*-
postgres specific registered procedures for the Bytes File System storage,
require the plpythonu language installed
*/
CREATE OR REPLACE FUNCTION _fsopen(bytea) RETURNS bytea AS $$
fpath = args[0]
if fpath:
try:
data = file(fpath, 'rb').read()
#/* XXX due to plpython bug we have to replace some characters... */
return data.replace("\\", r"\134").replace("\000", r"\000").replace("'", r"\047") #'
except Exception, ex:
plpy.warning('failed to get content for %s: %s', fpath, ex)
return None
$$ LANGUAGE plpythonu
/* WITH(ISCACHABLE) XXX does postgres handle caching of large data nicely */
;;
/* fspath(eid, entity type, attribute) */
CREATE OR REPLACE FUNCTION fspath(bigint, text, text) RETURNS bytea AS $$
pkey = 'plan%s%s' % (args[1], args[2])
try:
plan = SD[pkey]
except KeyError:
#/* then prepare and cache plan to get versioned file information from a
# version content eid */
plan = plpy.prepare(
'SELECT X.cw_%s FROM cw_%s as X WHERE X.cw_eid=$1' % (args[2], args[1]),
['bigint'])
SD[pkey] = plan
return plpy.execute(plan, [args[0]])[0]
$$ LANGUAGE plpythonu
/* WITH(ISCACHABLE) XXX does postgres handle caching of large data nicely */
;;