Thread: Re: Convert JSON value back to postgres representation

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.