Обсуждение: Convert JSON value back to postgres representation
Postgres has a to_jsonb function that will convert a value into its jsonb representation. I am now trying to turn a json value back into its postgres type. I was hoping there would be something like a from_jsonb function that, along with a type hint, could be used as an inverse of to_jsonb, like
from_jsonb(to_jsonb('{1,2,3}'::int[]) as int[]
but I do not see a function like this. I was able to convert a json value back to its postgres representation using the jsonb_to_record function, as used in the WHERE expression below, but I feel like there might be a better way to do this.
CREATE TABLE mytable (id int, col1 int[]);
INSERT INTO mytable VALUES (1, '{1, 2, 3}'), (2, '{3, 4, 5}');
SELECT * from mytable WHERE col1 = (select col1 from json_to_record('{"col1": [1, 2, 3]}'::JSON) as x(col1 int[]));
Thank you,
Phillip
On Thu, 2025-06-19 at 23:05 +0200, Phillip Diffley wrote:
> Postgres has a to_jsonb function that will convert a value into its jsonb representation.
> I am now trying to turn a json value back into its postgres type. I was hoping there would
> be something like a from_jsonb function that, along with a type hint, could be used as an
> inverse of to_jsonb, like
>
> from_jsonb(to_jsonb('{1,2,3}'::int[]) as int[]
>
> but I do not see a function like this. I was able to convert a json value back to its
> postgres representation using the jsonb_to_record function, as used in the WHERE expression
> below, but I feel like there might be a better way to do this.
>
> CREATE TABLE mytable (id int, col1 int[]);
> INSERT INTO mytable VALUES (1, '{1, 2, 3}'), (2, '{3, 4, 5}');
> SELECT * from mytable WHERE col1 = (select col1 from json_to_record('{"col1": [1, 2, 3]}'::JSON) as x(col1 int[]));
>
> Is there a preferred method for turning a JSON value back to its postgres representation?
I think jsonb_populate_record() is the closest thing to what you envision.
Not quite right, but:
CREATE TEMP TABLE arr(a integer[]);
SELECT * FROM jsonb_populate_record(
NULL::arr,
jsonb_build_object('a', to_jsonb(ARRAY[1, 2, 3]))
);
a
═════════
{1,2,3}
(1 row)
Yours,
Laurenz Albe
On Thursday, June 19, 2025, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
On Thu, 2025-06-19 at 23:05 +0200, Phillip Diffley wrote:
> Postgres has a to_jsonb function that will convert a value into its jsonb representation.
> I am now trying to turn a json value back into its postgres type. I was hoping there would
> be something like a from_jsonb function that, along with a type hint, could be used as an
> inverse of to_jsonb, like
>
> from_jsonb(to_jsonb('{1,2,3}'::int[]) as int[]
>
> but I do not see a function like this. I was able to convert a json value back to its
> postgres representation using the jsonb_to_record function, as used in the WHERE expression
> below, but I feel like there might be a better way to do this.
>
> CREATE TABLE mytable (id int, col1 int[]);
> INSERT INTO mytable VALUES (1, '{1, 2, 3}'), (2, '{3, 4, 5}');
> SELECT * from mytable WHERE col1 = (select col1 from json_to_record('{"col1": [1, 2, 3]}'::JSON) as x(col1 int[]));
>
> Is there a preferred method for turning a JSON value back to its postgres representation?
I think jsonb_populate_record() is the closest thing to what you envision.
jsonb_to_record avoids the temporary type.
select * from jsonb_to_record('{"ia":[1,2,3]}'::jsonb) as r (ia integer[]);
There is a gap for arrays. Scalars you can just cast and composites have these functions. But no simple/direct way to go from json array to sql array is presently implemented.
Though since 17 json_query can apparently do it.
select pg_typeof( json_query('[1,2,3]'::jsonb, '$' returning integer[]) ) -> integer[]
David J.