Delete form table doesn't work psql

Question

So I'm currently working on PostgreSQL (10.4) and need to simulate a "file system" within my database. In order to achieve this goal I have two tables :

-- represent a directory
CREATE TABLE USERS_DIRECTORIES
(
    id                  SERIAL          NOT NULL,
    users_id            INTEGER         NOT NULL,
    name                VARCHAR(64)     NOT NULL,
    description         VARCHAR(64)     NOT NULL DEFAULT '',
    created_at          TIMESTAMP WITH TIME ZONE        NOT NULL DEFAULT NOW(),
    UNIQUE(users_id, name),
    PRIMARY KEY (id),
    FOREIGN KEY (users_id) REFERENCES USERS(id)
);

-- represent links between a directory and its sub-directories
CREATE TABLE SUB_DIRECTORIES
(
    id                  SERIAL          NOT NULL,
    -- parent directory
    parent_id           INTEGER,
    -- sub directory
    child_id            INTEGER         NOT NULL,
    created_at          TIMESTAMP WITH TIME ZONE        NOT NULL DEFAULT NOW(),
    PRIMARY KEY (id),
    FOREIGN KEY (parent_id) REFERENCES USERS_DIRECTORIES(id),
    FOREIGN KEY (child_id) REFERENCES USERS_DIRECTORIES(id) ON DELETE CASCADE
);

The issue occur when I need to delete a directory. In order to do it correctly I need to delete all sub directories.

CURRENT SOLUTION

To delete a sub directory I need to delete its reference in the 'SUB_DIRECTORIES' tables to not trigger the foreign key exception. to solve this problem I use two triggered procedures.

-- triggered when I delete a directory to delete a reference 
CREATE OR REPLACE FUNCTION delete_reference()
RETURNS TRIGGER AS
$$
BEGIN
   raise notice 'OLD: %', OLD.id;
   DELETE FROM sub_directories WHERE parent_id = OLD.id;
   IF FOUND THEN 
      raise notice 'SUCESS id : %', OLD.id;
   END IF;
   RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER on_delete_sub_references BEFORE DELETE ON users_directories
    FOR EACH ROW
    EXECUTE PROCEDURE delete_reference();

-- triggered when I delete a reference to delete all sub directories
CREATE OR REPLACE FUNCTION delete_refered()
RETURNS TRIGGER AS
$$
BEGIN
    raise notice 'OLD child: %', OLD.child_id;
    DELETE FROM users_directories WHERE id = OLD.child_id;
    IF FOUND THEN 
         raise notice 'SUCESS child_id : %', OLD.child_id;
    END IF;
    RETURN NEW;
EXCEPTION
    WHEN OTHERS THEN
        raise notice 'EXCEPTION';
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER on_delete_sub_refered AFTER DELETE ON sub_directories
    FOR EACH ROW
    EXECUTE PROCEDURE delete_refered();

Whenever I delete a directory it triggers 'delete_reference()' function which remove all references of the directory from the tables 'SUB_DIRECTORIES' and when I delete a references from the very same table it triggers the 'delete_refered()' functions which delete the sub_directories and it goes on and on recursively.

PROBLEM

Evertything works fine except that no data is deleted in the table 'USERS_DIRECTORIES'. The references are deleted correctly in the 'SUB_DIRECTORIES' table tho. Eventhough I try to delete 'by hand' a specific row in the table 'USERS_DIRECTORIES' ('delete from ... where id = ..') it ends up with 'DELETE 0' with a correct query and id.

After much time asking Google for solutions I don't find anything about my issue. Moreover I'm not a native english speaker so it is hard to find good key words defining my problem. If anyone can help me on this one I'll be very grateful.

PS : I can speak french too if it helps.

Answer 1

RETURN OLD; for BEFORE DELETE trigger (this you have wrong), RETURN NEW; for AFTER DELETE.

You can also use OLD in AFTER DELETE triggers, so safest is to always return OLD in DELETE trigger.