Getting difference between two dates from 2 REF'd columns - sql

Question

I'm new to SQL and I'm trying to get the date between 2 values between two REF'd column values.
I currently have the tables set up like below:
CREATE OR REPLACE TYPE Person_Type AS OBJECT
(PersonId NUMBER,
DateBorn DATE)
CREATE OR REPLACE TYPE Movie_Type AS OBJECT
(MovieId NUMBER,
ReleaseDate DATE)
CREATE OR REPLACE TYPE Role_Type AS OBJECT
(PersonId REF Person_Type,
MovieId REF Movie_Type,
Name VARCHAR2(40),
MAP MEMBER FUNCTION Actor_Age RETURN NUMBER)
The data is inserted like this:
INSERT INTO Person_Table
VALUES (10000, '11-NOV-1974')
INSERT INTO Movie_Table
VALUES(1000000, '19-DEC-1997')
INSERT INTO Role_Table
VALUES((SELECT REF(a) FROM Person_Table a WHERE a.PersonId = 10000),
(SELECT REF(b) FROM Movie_Table b WHERE b.MovieId = 1000000),
'Some Person')
I'm trying to get the method Actor_Age to return the difference between the day someone is born and the date the movie got released. I've tried the below but it won't compile..
CREATE OR REPLACE TYPE BODY Role_Type
AS
MAP MEMBER FUNCTION Actor_Age
RETURN NUMBER
IS
BEGIN
RETURN (MONTHS_BETWEEN((SELECT g.PersonId.DateBorn FROM Role_Table g),
(SELECT f.MovieId.Releasedate FROM Role_Table f)/12));
END;
END;

Answer 1

SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE OR REPLACE TYPE Person_Type AS OBJECT
(PersonId NUMBER,
DateBorn DATE)
/
CREATE OR REPLACE TYPE Movie_Type AS OBJECT
(MovieId NUMBER,
ReleaseDate DATE)
/
CREATE OR REPLACE TYPE Role_Type AS OBJECT
(PersonId REF Person_Type,
MovieId REF Movie_Type,
Name VARCHAR2(40),
MAP MEMBER FUNCTION Actor_Age RETURN NUMBER)
/
CREATE OR REPLACE TYPE BODY Role_Type
AS
MAP MEMBER FUNCTION Actor_Age
RETURN NUMBER
IS
p_age NUMBER;
BEGIN
SELECT MONTHS_BETWEEN(
DEREF( MovieID ).ReleaseDate,
DEREF( PersonID ).DateBorn
) / 12
INTO p_age
FROM DUAL;
RETURN p_age;
END;
END;
/
CREATE TABLE Person_Table OF Person_Type
/
CREATE TABLE Movie_Table OF Movie_Type
/
CREATE TABLE Role_Table OF Role_Type
/
INSERT INTO Person_Table VALUES ( 10000, DATE '1970-01-01' )
/
INSERT INTO Movie_Table VALUES ( 1000000, DATE '2000-01-01' )
/
INSERT INTO Role_Table VALUES(
(SELECT REF(a) FROM Person_Table a WHERE a.PersonId = 10000),
(SELECT REF(b) FROM Movie_Table b WHERE b.MovieId = 1000000),
'Some Person'
)
/
Query 1:
SELECT Name,
r.Actor_Age()
FROM Role_table r
Results:
| NAME | R.ACTOR_AGE() |
|-------------|---------------|
| Some Person | 30 |

Answer 2

In pl sql you have to use construction select into
CREATE OR REPLACE TYPE BODY Role_Type
AS
MAP MEMBER FUNCTION Actor_Age
RETURN NUMBER
IS
v_date_born date ;
v_realse_date date ;
BEGIN
SELECT deref(self.PersonId).DateBorn into v_date_born FROM dual;
SELECT deref(self.MovieId).Releasedate into v_realse_date FROM dual;
RETURN (MONTHS_BETWEEN(v_date_born,v_realse_date)/12);
END;
END;