On 11/28/2012 08:16 PM, Hannu Krosing wrote:
On 11/29/2012 02:07 AM, Hannu Krosing wrote:
On 11/29/2012 01:10 AM, Merlin Moncure wrote:
On Wed, Nov 28, 2012 at 2:44 PM, Andrew Dunstan
<and...@dunslane.net> wrote:
...
*) have you considered something like
anyelement from_json(anyelement, json)
or
select <json>::some_type; (this may or many not be possible given
our
casting mechanics; i don't know).
I have no idea what the semantics of this would be.
Yeah, there's a lot of nuance there.
One way to tackle it would give the argument element as a template
and the result will the same template filled in from json filled
create table tab1(id serial primary key, ts timestamp default now(),
data text);
insert into tab1 select from_json(row(null,null,null)::tab1,
'{"data":"the data"}');
insert into tab1 select from_json(row(null,null,null)::tab1,
'{"id":-1, "ts":null, "data":""}');
insert into tab1 select from_json(t.*,'{"data":"more data"}') from
tab1 t where id = -1;
hannu=# select row_to_json(t.*) from tab1 t;
row_to_json
---------------------------------------------------------------
{"id":1,"ts":"2012-11-29 02:01:48.379172","data":"the data"}
{"id":-1,"ts":null, "data":""}
{"id":2,"ts":"2012-11-29 02:02:34.600164","data":"more data"}
(3 rows)
if extracting the defaults from table def proves too tricky for first
iteration, then
just set the missing fields to NULL or even better, carry over the
values from template;
You could even do a template-less row_from_json which returns a
records with all fields converted to
the JSON-encodable types and hope that the next conversions will be
done by postgreSQL as needed.
insert into tab1 select row_from_json('{"id":100, "ts":"2012-12-21",
"data":"End of Everything"}');
insert into tab1
select * from row_from_json(
'[{"id":101, "ts":"2012-12-22", "data":"1st day after End of Everything"}
{"id":102, "ts":"2012-12-22", "data":"2nd day after End of Everything"}
]');
The real problem here is that for any irregularly shaped json it's
likely to be a bust, and could only possibly work sanely for nested json
at all if the target type had corresponding array and composite fields.
hstore's populate_record works fairly well precisely because hstore is a
flat structure, unlike json.
In any case, I think this sort of suggestion highlights the possible
benefits of what I suggested upthread, namely to expose an API that will
allow easy construction of json transformation functions as extensions.
PS: good work so far :)
Hannu
Thanks.
cheers
andrew
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
