Postgres: user mapping not found for "postgres" - sql

Question

I'm connected to schema apm.
Trying to execute a function and getting below error:
ERROR: user mapping not found for "postgres"
Database connection info says:
apm on postgres#PostgreSQL 9.6
psql version: PostgreSQL 9.6.3, compiled by Visual C++ build 1800, 64-bit
How can this error be addressed?

Answer 1

It means that you are trying to use foreign table and your role (in this case postgres) does not have defined user and password for remote server.
You can add this by executing such query:
CREATE USER MAPPING
FOR postgres
SERVER remote_server_name
OPTIONS (user 'bob', password 'secret');
You can get server name for table like that:
SELECT srvname
FROM pg_foreign_table t
JOIN pg_foreign_server s ON s.oid = t.ftserver
WHERE ftrelid = 'schemaname.tablename'::regclass

Answer 2

If you want to create user mapping for all users, you can do it like this
CREATE USER MAPPING
FOR PUBLIC
SERVER remote_server_name
OPTIONS (user 'bob', password 'secret');

Answer 3

https://www.postgresql.org/docs/current/static/sql-createusermapping.html
CREATE USER MAPPING — define a new mapping of a user to a foreign
server
Your function queries foreign tables, using some server, for which you need a user mapping. Apparently it exists for the user owner, and not for you. Or just run the function with a user that has user mapping created.
you can view them with:
SELECT um.*,rolname
FROM pg_user_mapping um
JOIN pg_roles r ON r.oid = umuser
JOIN pg_foreign_server fs ON fs.oid = umserver;