SET timezone TO 'Etc/UTC';
SELECT sparql.add_context('testctx', 'test context');
 add_context 
-------------
 
(1 row)

SELECT sparql.add_prefix('testctx', 'foo', 'http://example.org/foo#');
 add_prefix 
------------
 
(1 row)

SELECT sparql.add_prefix('testctx', 'bar', 'http://example.org/bar#');
 add_prefix 
------------
 
(1 row)

CREATE SERVER wikidata
FOREIGN DATA WRAPPER rdf_fdw 
OPTIONS (
  endpoint 'https://query.wikidata.org/sparql',
  prefix_context 'testctx');
CREATE FOREIGN TABLE rdbms (
  p rdfnode OPTIONS (variable '?l'),
  o rdfnode OPTIONS (variable '?cr')
)
SERVER wikidata OPTIONS (
  log_sparql 'true',
  sparql '
  prefix wd: <http://www.wikidata.org/entity/>   PreFiX skos:         <http://www.w3.org/2004/02/skos/core#>

PREFIX        wdt: <http://www.wikidata.org/prop/direct/>


SELECT * {
  ?s skos:altLabel ?l .
  ?s wdt:P6216 ?cr
  FILTER (?s = wd:Q192490)
  FILTER (LANG(?l) ="en")
}');
-- Prefixes configured in the default context added
-- and existing prefixes formatted
SELECT p, o FROM rdbms ORDER BY p::text COLLATE "C";
INFO:  SPARQL query sent to 'https://query.wikidata.org/sparql':
PREFIX foo: <http://example.org/foo#>
PREFIX bar: <http://example.org/bar#>
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>

SELECT ?l ?cr 
{
  ?s skos:altLabel ?l .
  ?s wdt:P6216 ?cr
  FILTER (?s = wd:Q192490)
  FILTER (LANG(?l) ="en")
}

INFO:  SPARQL returned 1 record.

       p       |                     o                      
---------------+--------------------------------------------
 "Postgres"@en | <http://www.wikidata.org/entity/Q50423863>
(1 row)

ALTER SERVER wikidata OPTIONS (SET prefix_context 'foo');
-- Prefix context does not exist. Issuing a WARNING.
SELECT p, o FROM rdbms ORDER BY p::text COLLATE "C";
WARNING:  no prefixes found for context 'foo'
INFO:  SPARQL query sent to 'https://query.wikidata.org/sparql':
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>

SELECT ?l ?cr 
{
  ?s skos:altLabel ?l .
  ?s wdt:P6216 ?cr
  FILTER (?s = wd:Q192490)
  FILTER (LANG(?l) ="en")
}

INFO:  SPARQL returned 1 record.

       p       |                     o                      
---------------+--------------------------------------------
 "Postgres"@en | <http://www.wikidata.org/entity/Q50423863>
(1 row)

-- No prefix context set. Using only prefixes from the
-- SPARQL query.
ALTER SERVER wikidata OPTIONS (DROP prefix_context);
SELECT p, o FROM rdbms ORDER BY p::text COLLATE "C";
INFO:  SPARQL query sent to 'https://query.wikidata.org/sparql':
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>

SELECT ?l ?cr 
{
  ?s skos:altLabel ?l .
  ?s wdt:P6216 ?cr
  FILTER (?s = wd:Q192490)
  FILTER (LANG(?l) ="en")
}

INFO:  SPARQL returned 1 record.

       p       |                     o                      
---------------+--------------------------------------------
 "Postgres"@en | <http://www.wikidata.org/entity/Q50423863>
(1 row)

\set VERBOSITY terse
-- Add existing context and prefix (must fail)
SELECT sparql.add_context('testctx', 'test context');
ERROR:  prefix context "testctx" already exists
SELECT sparql.add_prefix('testctx', 'foo', 'http://example.org/foo#');
ERROR:  prefix "testctx" already exists in context "foo"
-- Add existing context and prefix forcing overwrite
SELECT sparql.add_context('testctx', 'test context - updated', true);
 add_context 
-------------
 
(1 row)

SELECT sparql.add_prefix('testctx', 'foo', 'http://example.org/foo-updated#', true);
 add_prefix 
------------
 
(1 row)

-- Check the prefix context and prefixes
SELECT context, description FROM sparql.prefix_contexts ORDER BY context COLLATE "C";
 context |             description             
---------+-------------------------------------
 default | Default context for SPARQL prefixes
 testctx | test context - updated
(2 rows)

SELECT context, prefix, uri FROM sparql.prefixes ORDER BY context, prefix COLLATE "C";
 context | prefix |                     uri                     
---------+--------+---------------------------------------------
 default | dc     | http://purl.org/dc/elements/1.1/
 default | foaf   | http://xmlns.com/foaf/0.1/
 default | owl    | http://www.w3.org/2002/07/owl#
 default | rdf    | http://www.w3.org/1999/02/22-rdf-syntax-ns#
 default | rdfs   | http://www.w3.org/2000/01/rdf-schema#
 default | xsd    | http://www.w3.org/2001/XMLSchema#
 testctx | bar    | http://example.org/bar#
 testctx | foo    | http://example.org/foo-updated#
(8 rows)

-- Drop prefix
SELECT sparql.drop_prefix('testctx', 'foo');
 drop_prefix 
-------------
 
(1 row)

SELECT context, prefix, uri FROM sparql.prefixes WHERE context = 'testctx' ORDER BY prefix COLLATE "C";
 context | prefix |           uri           
---------+--------+-------------------------
 testctx | bar    | http://example.org/bar#
(1 row)

-- Drop context forcing cascade
SELECT sparql.drop_context('testctx', true);
 drop_context 
--------------
 
(1 row)

SELECT context, description FROM sparql.prefix_contexts ORDER BY context COLLATE "C";
 context |             description             
---------+-------------------------------------
 default | Default context for SPARQL prefixes
(1 row)

SELECT context, prefix, uri FROM sparql.prefixes ORDER BY context, prefix COLLATE "C";
 context | prefix |                     uri                     
---------+--------+---------------------------------------------
 default | dc     | http://purl.org/dc/elements/1.1/
 default | foaf   | http://xmlns.com/foaf/0.1/
 default | owl    | http://www.w3.org/2002/07/owl#
 default | rdf    | http://www.w3.org/1999/02/22-rdf-syntax-ns#
 default | rdfs   | http://www.w3.org/2000/01/rdf-schema#
 default | xsd    | http://www.w3.org/2001/XMLSchema#
(6 rows)

DROP SERVER wikidata CASCADE;
NOTICE:  drop cascades to foreign table rdbms