Re: Convert JSON value back to postgres representation

From: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
To: Phillip Diffley <phillip6402(at)gmail(dot)com>, pgsql-general(at)postgresql(dot)org
Subject: Re: Convert JSON value back to postgres representation
Date: 2025-06-20 04:59:41
Message-ID: b9ffb897998ec715ff5ced0204e9f89631d260da.camel@cybertec.at
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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

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