Re: Emitting JSON to file using COPY TO

jian he <jian.universality@gmail.com>

From: jian he <jian.universality@gmail.com>

To: Joe Conway <mail@joeconway.com>

Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, Daniel Verite <daniel@manitou-mail.org>, Andrew Dunstan <andrew@dunslane.net>, Davin Shearer <davin@apache.org>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2024-01-16T03:46:59Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Add option force_array for COPY JSON FORMAT
- 4c0390ac53b7 19 (unreleased) landed
json format for COPY TO
- 7dadd38cda95 19 (unreleased) landed
introduce CopyFormat, refactor CopyFormatOptions
- a2145605ee3d 19 (unreleased) landed
Doc: add IDs to copy.sgml's <varlistentry> and <refsect1>
- e4018f891dec 19 (unreleased) cited

Attachments

test.sql (application/sql)
patch.out (application/octet-stream)
patch_bless_twice.out (application/octet-stream)

On Tue, Jan 9, 2024 at 4:40 AM Joe Conway <mail@joeconway.com> wrote:
>
> On 1/8/24 14:36, Dean Rasheed wrote:
> > On Thu, 7 Dec 2023 at 01:10, Joe Conway <mail@joeconway.com> wrote:
> >>
> >> The attached should fix the CopyOut response to say one column.
> >>
> >
> > Playing around with this, I found a couple of cases that generate an error:
> >
> > COPY (SELECT 1 UNION ALL SELECT 2) TO stdout WITH (format json);
> >
> > COPY (VALUES (1), (2)) TO stdout WITH (format json);
> >
> > both of those generate the following:
> >
> > ERROR:  record type has not been registered
>
>
> Thanks -- will have a look
>
> --
> Joe Conway
> PostgreSQL Contributors Team
> RDS Open Source Databases
> Amazon Web Services: https://aws.amazon.com
>
>
>

In the function CopyOneRowTo, I try to call the function BlessTupleDesc again.

+BlessTupleDesc(slot->tts_tupleDescriptor);
rowdata = ExecFetchSlotHeapTupleDatum(slot);

Please check the attachment. (one test.sql file, one patch, one bless twice).

Now the error cases are gone, less cases return error.
but the new result is not the expected.

`COPY (SELECT g from generate_series(1,1) g) TO stdout WITH (format json);`
returns
{"":1}
The expected result would be `{"g":1}`.

I think the reason is maybe related to the function copy_dest_startup.