"cannot assign non-composite value to a record variable " while storing result in array - postgresql

Question

on Postgres 13 I have a trigger execute ON UPDATE of a table. In this trigger I want to store in an array a result from a query, because I will need to use it inside an inner iterator, multiple times. In this way I avoid performing the same query at every iteration and I can reuse the array.
At first I tried like this, I typed the variable as array record:
create or REPLACE FUNCTION check_companyprofile_between_records_constraints_trigger_hook()
RETURNS trigger as
$body$
declare
l_table1_results record[];
l_table1_result record;
l_record record;
begin
l_table1_results := ARRAY(
select
date_start,
coalesce(date_end, 'infinity'::date) as date_end
FROM application.section_profile_company_metadata
WHERE persona_id = NEW.persona_id and id != new.id
);
for l_record in (
select foo,bar,baz
from table2
)
loop
foreach l_table1_result in array l_table1_results
loop
-- Check some stuffs
end loop;
end loop;
RETURN NEW;
end
$body$
LANGUAGE plpgsql;
But I'm getting a
Errore SQL [0A000]: ERROR: variable "l_table1_results" has pseudo-type record[]
Doing some research I discovered it is not possible to assign an in-memory variable with the result of a query, but instead I need to use a custom type. Ok, so I tried also this
create type apc_dates_pair as (
date_start date,
date_end date
);
create or REPLACE FUNCTION check_companyprofile_between_records_constraints_trigger_hook()
RETURNS trigger as
$body$
declare
l_table1_results apc_dates_pair[];
l_table1_result record;
l_record record;
begin
l_table1_results := ARRAY(
select
date_start,
coalesce(date_end, 'infinity'::date) as date_end
FROM application.section_profile_company_metadata
WHERE persona_id = NEW.persona_id and id != new.id
);
-- TODO do some stuffs with array
for l_record in (
select foo,bar,baz
from table2
)
loop
foreach l_table1_result in l_table1_results
loop
-- Check some stuffs
end loop;
end loop;
RETURN NEW;
end
$body$
LANGUAGE plpgsql;
create or REPLACE FUNCTION check_companyprofile_between_records_constraints_trigger_hook()
RETURNS trigger as
$body$
declare
l_table1_results apc_dates_pair[];
l_table1_result record;
l_record record;
begin
l_table1_results := ARRAY(
select row(
date_start,
coalesce(date_end, 'infinity'::date)
)
FROM application.section_profile_company_metadata
WHERE persona_id = NEW.persona_id and id != new.id
);
for l_record in (
select foo,bar,baz
from table2
)
loop
foreach l_table1_result in array l_table1_results
loop
-- Check some stuffs
end loop;
end loop;
RETURN NEW;
end
$body$
LANGUAGE plpgsql;
Different error, but still an error:
cannot assign non-composite value to a record variable
And from this I did not find much.
Is it possible at all to store a temp query inside and array of records and then iterate them?

Answer 1

An explanation more then an answer:
You seem to be confusing composite types with arrays, they are different things in Postgres. Most notably a Postgres Array contains values of a single type. You can have int[] all integers, varchar[] all characters, and so on, but you cannot mix types in a single array. A Composite Type on the other hand can do just that, have included values that are of different types. In plpgsql declaring a record is to basically declare an anonymous composite type that acquires the properties of whatever actual composite type is passed to it. This is why you get your second error; "cannot assign non-composite value to a record variable". You are trying to assign an array to a composite type, in this case a record. Given that the values you want to store are both dates you could dispense with create type apc_dates_pair ... and just do l_table1_results date[]. Then iterate over the array using the form shown at Array loop.