Please be sure to include single and double quotes in the test values since that was the original problem (double quoting in COPY TO breaking the JSON syntax).
On 2023-12-01 Fr 14:28, Joe Conway wrote: > On 11/29/23 10:32, Davin Shearer wrote: >> Thanks for the responses everyone. >> >> I worked around the issue using the `psql -tc` method as Filip >> described. >> >> I think it would be great to support writing JSON using COPY TO at >> some point so I can emit JSON to files using a PostgreSQL function >> directly. >> >> -Davin >> >> On Tue, Nov 28, 2023 at 2:36 AM Filip Sedlák <filip@sedlakovi.org >> <mailto:filip@sedlakovi.org>> wrote: >> >> This would be a very special case for COPY. It applies only to a >> single >> column of JSON values. The original problem can be solved with psql >> --tuples-only as David wrote earlier. >> >> >> $ psql -tc 'select json_agg(row_to_json(t)) >> from (select * from public.tbl_json_test) t;' >> >> [{"id":1,"t_test":"here's a \"string\""}] >> >> >> Special-casing any encoding/escaping scheme leads to bugs and harder >> parsing. > > (moved to hackers) > > I did a quick PoC patch (attached) -- if there interest and no hard > objections I would like to get it up to speed for the January commitfest. > > Currently the patch lacks documentation and regression test support. > > Questions: > ---------- > 1. Is supporting JSON array format sufficient, or does it need to > support some other options? How flexible does the support scheme need > to be? > > 2. This only supports COPY TO and we would undoubtedly want to support > COPY FROM for JSON as well, but is that required from the start? > > Thanks for any feedback.
I realize this is just a POC, but I'd prefer to see composite_to_json() not exposed. You could use the already public datum_to_json() instead, passing JSONTYPE_COMPOSITE and F_RECORD_OUT as the second and third arguments.
I think JSON array format is sufficient.
I can see both sides of the COPY FROM argument, but I think insisting on that makes this less doable for release 17. On balance I would stick to COPY TO for now.