json_populate_recordset

2018-06-07 18:51 GMT+02:00 Adrian Klaver <adrian.klaver@aklaver.com>:

From here:

https://www.postgresql.org/docs/10/static/functions-json.html

select * from json_populate_record(null::myrowtype, '{"a": 1, "b": ["2",
"a b"], "c": {"d": 4, "e": "a b c"}}')

What is the null::myrowtype doing?

this function uses polymorphic parameters - its some like

create or replace function fx(in anyelement, json) returns anyelement ..

output polymorphic value requires minimally one input polymorphic value for
type specification. Postgres has not possibility to pass only datatype - so
pattern null:type is used instead.

Regards

Pavel

On 06/07/2018 09:56 AM, Pavel Stehule wrote:

2018-06-07 18:51 GMT+02:00 Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>>:

From here:

https://www.postgresql.org/docs/10/static/functions-json.html
<https://www.postgresql.org/docs/10/static/functions-json.html&gt;

select * from json_populate_record(null::myrowtype, '{"a": 1, "b":
["2", "a b"], "c": {"d": 4, "e": "a b c"}}')

What is the null::myrowtype doing?

this function uses polymorphic parameters - its some like

create or replace function fx(in anyelement, json) returns anyelement ..

output polymorphic value requires minimally one input polymorphic value
for type specification. Postgres has not possibility to pass only
datatype - so pattern null:type is used instead.

Alright, so it is bootstrapping a polymorphic type off null. Thanks.

Regards

Pavel

Thanks,
--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

--
Adrian Klaver
adrian.klaver@aklaver.com