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# Graffiti RDF Store
# (originally written for Samizdat project)
#
# Copyright (c) 2002-2011 Dmitry Borodaenko <angdraug@debian.org>
#
# This program is free software.
# You can distribute/modify this program under the terms of
# the GNU General Public License version 3 or later.
#
# see doc/rdf-storage.txt for introduction and Graffiti Squish definition;
# see doc/storage-impl.txt for explanation of implemented algorithms
#
# vim: et sw=2 sts=2 ts=8 tw=0
require 'syncache'
require 'graffiti/exceptions'
require 'graffiti/debug'
require 'graffiti/rdf_config'
require 'graffiti/squish'
module Graffiti
# API for the RDF storage access similar to DBI or Sequel
#
class Store
# initialize class attributes
#
# _db_ is a Sequel database handle
#
# _config_ is a hash of configuraiton options for RdfConfig
#
def initialize(db, config)
@db = db
@config = RdfConfig.new(config)
# cache parsed Squish SELECT queries
@select_cache = SynCache::Cache.new(nil, 1000)
end
# storage configuration in an RdfConfig object
#
attr_reader :config
# replace schema uri with a prefix from the configured namespaces
#
def ns_shrink(uriref)
SquishQuery.ns_shrink(uriref, @config.ns)
end
# get value of subject's property
#
def get_property(subject, property)
fetch(%{SELECT ?object WHERE (#{property} :subject ?object)},
:subject => subject).get(:object)
end
def fetch(query, params={})
@db.fetch(select(query), params)
end
# get one query answer (similar to DBI#select_one)
#
def select_one(query, params={})
fetch(query, params).first
end
# get all query answers (similar to DBI#select_all)
#
def select_all(query, limit=nil, offset=nil, params={}, &p)
ds = fetch(query, params).limit(limit, offset)
if block_given?
ds.all(&p)
else
ds.all
end
end
# accepts String or pre-parsed SquishQuery object, caches SQL by String
#
def select(query)
query.kind_of?(String) and
query = @select_cache.fetch_or_add(query) { SquishSelect.new(@config, query) }
query.kind_of?(SquishSelect) or raise ProgrammingError,
"String or SquishSelect expected"
query.to_sql
end
# merge Squish query into RDF database
#
# returns list of new ids assigned to blank nodes listed in INSERT section
#
def assert(query, params={})
@db.transaction do
SquishAssert.new(@config, query).run(@db, params)
end
end
end
end
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