spock.lo_manage trigger function to manage Large Objects with example usage

README.md

@@ -130,6 +130,54 @@ lolor_db=# SELECT lo_unlink (1100449);
 (1 row)
 ```
 
+## Manage large objects
+
+`lolor` extension provide support for managing Large Objects similar to PostgreSQL native `lo` module. `spock.lo_manage` trigger function
+can be used with trigger by attached tables that contain `LO` reference columns.
+
+### Example usage
+
+```
+CREATE EXTENSION lolor;
+
+-- example table and data
+CREATE TABLE lotest(a INT PRIMARY KEY,
+	b OID
+);
+
+INSERT INTO lotest
+	VALUES (1, lo_import('/etc/os-release'));
+
+-- check the large object oid
+test_db=# SELECT * FROM lotest;
+ a |   b    
+---+--------
+ 1 | 412833
+(1 row)
+
+-- verify large object oid 
+test_db=# SELECT * FROM lolor.pg_largeobject_metadata WHERE oid = 412833;
+  oid   | lomowner | lomacl 
+--------+----------+--------
+ 412833 |    16384 | 
+(1 row)
+
+-- manage table and cleanup to avoid orphen large object
+CREATE TRIGGER t_lotest BEFORE UPDATE OR DELETE ON lotest
+    FOR EACH ROW EXECUTE FUNCTION lolor.lo_manage(b);
+
+-- delete table record related to large object
+test_db=# DELETE FROM lotest WHERE a = 1;
+NOTICE:  trigger t_lotest: (delete) removing large object oid 412833
+DELETE 1
+
+-- related large object also deleted with the table record
+test_db=# SELECT * FROM lolor.pg_largeobject_metadata where oid = 412833;
+ oid | lomowner | lomacl 
+-----+----------+--------
+(0 rows)
+```
+
 ## Limitations
 
 - Native large object functionality cannot be used while you are using the lolor extension.

lolor--1.0.sql

@@ -188,4 +188,51 @@ CREATE FUNCTION pg_catalog.lo_on_drop_extension()
 CREATE EVENT TRIGGER lo_on_drop_extension
 	ON ddl_command_start WHEN tag IN ('DROP EXTENSION')
 	EXECUTE FUNCTION pg_catalog.lo_on_drop_extension();
-ALTER EVENT TRIGGER lo_on_drop_extension ENABLE ALWAYS;
+ALTER EVENT TRIGGER lo_on_drop_extension ENABLE ALWAYS;
+
+/*
+	clean up large object to avoid orphan large objects that are
+	no more associated with any table row in case of DELETE or UPDATE
+	operations
+*/
+CREATE FUNCTION lolor.lo_manage()
+	RETURNS TRIGGER
+AS $lo_manage$
+DECLARE
+   loid_old oid;
+   loid_new oid;
+BEGIN
+	-- handle UPDATE or DELETE operation only
+	IF TG_OP != 'UPDATE' AND
+		TG_OP != 'DELETE' THEN
+		RAISE EXCEPTION 'Trigger function LO_MANAGE should be fired for UPDATE OR DELETE only';
+	END IF;
+
+	IF TG_NARGS < 1 THEN
+		RAISE EXCEPTION 'trigger %: no column name provided in the trigger definition', TG_NAME;
+	END IF;
+	IF TG_LEVEL != 'ROW' THEN
+		RAISE EXCEPTION 'trigger % should be fired for row', TG_NAME;
+	END IF;
+	IF NOT to_jsonb(OLD)?TG_ARGV[0] THEN
+		RAISE EXCEPTION 'trigger %: column "%" does not exist', TG_NAME, TG_ARGV[0];
+	END IF;
+
+	loid_old = (row_to_json(OLD)->>TG_ARGV[0])::oid;
+	loid_new = (row_to_json(NEW)->>TG_ARGV[0])::oid;
+	IF TG_OP = 'UPDATE' THEN
+		IF loid_old IS NOT NULL AND
+			(loid_old != loid_new OR loid_new IS NULL) THEN
+			-- take care of updated rows operation, in case large object id changes
+			RAISE NOTICE 'trigger %: (update) removing large object oid %', TG_NAME, loid_old;
+			PERFORM lo_unlink(loid_old);
+		END IF;
+		RETURN NEW;
+	ELSIF TG_OP = 'DELETE' THEN
+		-- take care of deleted row operation
+		RAISE NOTICE 'trigger %: (delete) removing large object oid %', TG_NAME, loid_old;
+		PERFORM lo_unlink(loid_old);
+		RETURN OLD;
+	END IF;
+END;
+$lo_manage$ LANGUAGE PLPGSQL;