Pass the query result to the function - postgresql

Question

I created a function that takes as a parameter a string by which i am looking for the desired element in the Bus table. After that i create a trigger that will fire after inserting into the Maintenance table. Here i have a problem: i specify that when changing the table, call the function and pass the last added element there, but the trigger is not created.
I looked for similar questions and saw that you need to take the query in brackets, but it did not help.
Ask for your help!
Function:
create function set_status(model_ varchar(50)) returns void as $$
update Bus set technical_condition = 'don`t work' where model = model_;
$$ LANGUAGE sql;
Trigger:
create trigger check_insert
after insert on Maintenance
for each row
execute procedure set_status((select model from Maintenance order by id_m desc limit 1));

Answer 1

First off your trigger function must be of the form:
create or replace function <function_name>()
returns trigger
language plpgsql
as $$
begin
...
end;
$$;
The language specification may come either before the code or after it. Moreover it must be defined returning trigger and as taking no parameters. See documentation.
You can achieve what you want by moving the select status ... query into the trigger function itself.
create or replace function set_status()
returns trigger
language plpgsql
as $$
begin
update bus
set technical_condition =
(select model
from maintenance
order by id_m desc
limit 1
) ;
return null;
end;
$$;
create trigger check_insert
after insert on maintenance
for each row
execute procedure set_status();
NOTE: Not Tested.