indexed range queries on jsonb?

Hi,

I'm trying to find a way to do a range query on json such that it will use
an index. This seems possible given that jsonb supports btrees and
expression indices.

For example I have:

create index t1 on document using btree ((payload->'intTest'));

where: payload is a jsonb column and intTest is a json key whose value is
always an int. Based on the documentation examples, I created an index like
this:

create index t1 on document using btree ((payload->'intTest'));

Logically, what I want is to be able to make queries like this:

select * from document where ((payload->'intTest'))> 5;

With casting, I came up with:

select * from document where (((payload->'intTest'))::text)::integer > 5;

But this query does not use the index according to Explain

"Seq Scan on public.document (cost=0.00..1868.33 rows=5764 width=619)
(actual time=286.228..1706.638 rows=1974 loops=1)"
" Output: owner, document_type, guid, schema_version, payload,
last_update, payload_class, instance_version, acl_read, deleted, fts_text"
" Filter: ((((document.payload -> 'intTest'::text))::text)::integer > 5)"
" Rows Removed by Filter: 15319"
" Buffers: shared hit=5420 read=29085"
"Planning time: 0.108 ms"
"Execution time: 1706.941 ms"

Any help at all would be appreciated.

Thanks.