Allow subscripting of hstore values.

This is basically a finger exercise to prove that it's possible for
an extension module to add subscripting ability.  Subscripted fetch
from an hstore is not different from the existing "hstore -> text"
operator.  Subscripted update does seem to be a little easier to
use than the traditional update method using hstore concatenation,
but it's not a fundamentally new ability.

However, there may be some value in the code as sample code, since
it shows what's basically the minimum-complexity way to implement
subscripting when one needn't consider nested container objects.

Discussion: https://postgr.es/m/3724341.1607551174@sss.pgh.pa.us

1 files changed, 8 insertions, 0 deletions

diff --git a/contrib/hstore/sql/hstore.sql b/contrib/hstore/sql/hstore.sql
index a6c2f3a0ce..8d96e30403 100644
--- a/contrib/hstore/sql/hstore.sql
+++ b/contrib/hstore/sql/hstore.sql
@@ -364,6 +364,14 @@ insert into test_json_agg values ('rec1','"a key" =>1, b => t, c => null, d=> 12
 select json_agg(q) from test_json_agg q;
 select json_agg(q) from (select f1, hstore_to_json_loose(f2) as f2 from test_json_agg) q;
 
+-- Test subscripting
+insert into test_json_agg default values;
+select f2['d'], f2['x'] is null as x_isnull from test_json_agg;
+select f2['d']['e'] from test_json_agg;  -- error
+select f2['d':'e'] from test_json_agg;  -- error
+update test_json_agg set f2['d'] = f2['e'], f2['x'] = 'xyzzy';
+select f2 from test_json_agg;
+
 -- Check the hstore_hash() and hstore_hash_extended() function explicitly.
 SELECT v as value, hstore_hash(v)::bit(32) as standard,
        hstore_hash_extended(v, 0)::bit(32) as extended0,