如何获取function中某行的主键值？

Question

I have a function in postgres that sends events on CRUD operations in my tables. However the problem is that it only works for tables that have an id column which is the primary key. How can I change this so that I can use whatever column is the primary key?

CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
SET search_path = PUBLIC,
pg_catalog;
CREATE OR REPLACE FUNCTION psycopg2_pgevents_create_event() RETURNS TRIGGER AS $function$
  BEGIN
    IF (TG_OP = 'DELETE') THEN
        PERFORM pg_notify('psycopg2_pgevents_channel',
        json_build_object(
            'event_id', uuid_generate_v4(),
            'event_type', TG_OP,
            'schema_name', TG_TABLE_SCHEMA,
            'table_name', TG_TABLE_NAME,
            'row_id', OLD.id            -------- this is not always "id"
        )::text
     );
         RETURN NULL;
    ELSE
        raise notice 'Value: %', NEW;
        PERFORM pg_notify('psycopg2_pgevents_channel',
            json_build_object(
                'event_id', uuid_generate_v4(),
                'event_type', TG_OP,
                'schema_name', TG_TABLE_SCHEMA,
                'table_name', TG_TABLE_NAME,
                'row_id', NEW.id,         -------- this is not always "id"
                'data', NEW
        )::text
    );
    RETURN NULL;
    END IF;
  END;
$function$ LANGUAGE PLPGSQL;
SET search_path = "$user",
    PUBLIC;

Answer 1

If you only have a single primary key column, and you just want its value, you can extract it using:

to_jsonb(NEW)->>(
  SELECT attname
  FROM pg_attribute
  JOIN pg_index ON indexrelid = attrelid
  WHERE indrelid = TG_RELID
    AND indisprimary
)

If you've got multiple primary key columns, and/or you want to retrieve the PK in {"key":"value"} format, you could use:

SELECT jsonb_object_agg(attname, to_jsonb(NEW)->attname)
FROM pg_attribute
JOIN pg_index ON indexrelid = attrelid
WHERE indrelid = TG_RELID
  AND indisprimary