Re: search_path for PL/pgSQL functions partially cached?

On 1/3/25 15:22, Jan Behrens wrote:
> On Fri, 3 Jan 2025 13:56:02 -0800
> Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> wrote:
>
>> At this point I am lost as to what the overall goal of this is.
>>
>> Can you provide a 10000 ft view if what it is you are trying to achieve?
>
> Sure! I would like to create a component (e.g. a PostgreSQL extension)
> that provides a function which processes some complex data, without
> making any requirements regarding where the data is stored. To pass
> this data to the function, I could use arrays of composite types, but
> that seems to be very bulky. Another option would be to use cursors,
> but that didn't turn out to work very smooth either.
>
> Instead, I plan to expect the function to receive a query string that
> will get the data that is being processed by the function.
>
> That query string should be allowed to refer to tables in the
> search_path at the caller's side.
>
> Therefore, I cannot use the "SET search_path FROM CURRENT" in my
> "CREATE FUNCTION" statement, because it would overwrite the current
> search_path on each call of the function.
>
> Thus my idea is to do this (simplified):
>
> CREATE FUNCTION "some_function" ("query_p" TEXT) RETURNS "some_type"
>
> --------------------------------------------------------------------
> -- I cannot use SET search_path FROM CURRENT here, because "query_p"
> -- shall refer to tables in the search_path of the caller.
> --------------------------------------------------------------------
>
> LANGUAGE plpgsql AS $$
> DECLARE
> "old_search_path" TEXT;
>
> ----------------------------------------------------------------
> -- I have to fully qualify types in the DECLARE section.
> ----------------------------------------------------------------
>
> "some_variable" "some_schema"."some_type";
> BEGIN
> SELECT current_setting('search_path') INTO "old_search_path";
> PERFORM set_config(
> 'search_path',
> 'some_schema, pg_temp, ' || "old_search_path",
> TRUE
> );
>
> ----------------------------------------------------------------
> -- Do I have to fully qualify types and operators from
> -- "myschema" here? Or is it safe to not fully qualify them?
> ----------------------------------------------------------------
> END;
> $$;
>
> That is my overall idea.

Is 'some_schema' a known item when installing?

Once you have the search_path defined and assuming all the objects you
want are in that path, then yes you can drop the schema qualification.

>
> My problem is that I'm confused about WHEN EXACTLY I have to qualify
> tables/types, etc. It is very hard to understand from reading (just) the
> documentation.

If you are doing this as an extension then I suspect you want the
processes shown here:

https://www.postgresql.org/docs/17/extend-extensions.html#EXTEND-EXTENSIONS-RELOCATION

>
> Kind Regards,
> Jan Behrens

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com