Re: jsonb_strip_nulls with arrays?

On Tue, Sep 17, 2024 at 5:11 PM Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:

>
> On 2024-09-17 Tu 5:26 AM, Florents Tselai wrote:
>
> Currently:
>
>
> jsonb_strip_nulls ( jsonb ) → jsonb
>
> Deletes all object fields that have null values from the given JSON value,
> recursively. Null values that are not object fields are untouched.
>
>
> > Null values that are not object fields are untouched.
>
>
> Can we revisit this and make it work with arrays, too?
>
> Tbh, at first sight that looked like the expected behavior for me.
>
> That is strip nulls from arrays as well.
>
>
> This has been available since 9.5 and iiuc predates lots of the jsonb
> array work.
>
>
> I don't think that's a great idea. Removing an object field which has a
> null value shouldn't have any effect on the surrounding data, nor really
> any on other operations (If you try to get the value of the missing field
> it should give you back null). But removing a null array member isn't like
> that at all - unless it's the trailing member of the array it will renumber
> all the succeeding array members.
>
> And I don't think we should be changing the behaviour of a function, that
> people might have been relying on for the better part of a decade.
>
>
>
> In practice, though, whenever jsonb_build_array is used (especially with
> jsonpath),
>
> a few nulls do appear in the resulting array most of the times,
>
> Currently, there’s no expressive way to remove this.
>
>
> We could also have jsonb_array_strip_nulls(jsonb) as well
>
>
> We could, if we're going to do anything at all in this area. Another
> possibility would be to provide a second optional parameter for
> json{b}_strip_nulls. That's probably a better way to go.
>
Here's a patch that adds that argument (only for jsonb; no json
implementation yet)

That's how I imagined & implemented it,
but there may be non-obvious pitfalls in the semantics.

as-is version

select jsonb_strip_nulls('[1,2,null,3,4]');
jsonb_strip_nulls
--------------------
[1, 2, null, 3, 4]
(1 row)

select
jsonb_strip_nulls('{"a":1,"b":null,"c":[2,null,3],"d":{"e":4,"f":null}}');
jsonb_strip_nulls
--------------------------------------------
{"a": 1, "c": [2, null, 3], "d": {"e": 4}}
(1 row)

with the additional boolean flag added

select jsonb_strip_nulls('[1,2,null,3,4]', *true*);
jsonb_strip_nulls
-------------------
[1, 2, 3, 4]
(1 row)

select
jsonb_strip_nulls('{"a":1,"b":null,"c":[2,null,3],"d":{"e":4,"f":null}}',
*true*);
jsonb_strip_nulls
--------------------------------------
{"a": 1, "c": [2, 3], "d": {"e": 4}}
(1 row)

GH PR view: https://github.com/Florents-Tselai/postgres/pull/6/files

> cheers
>
>
> andrew
>
>
> --
> Andrew Dunstan
> EDB: https://www.enterprisedb.com
>
>