Object Types

Remarks#

It is important to note that an object body may not always be necessary. If the default constructor is sufficient, and no other functionality needs to be implemented then it should not be created.

A default constructor is the Oracle supplied constructor, which consists of all attributes listed in order of declaration. For example, an instance of BASE_TYPE could be constructed by the following call, even though we do not explicitly declare it.

l_obj := BASE_TYPE(1, 'Default', 1);

BASE_TYPE

Type declaration:

CREATE OR REPLACE TYPE base_type AS OBJECT
(
   base_id     INTEGER,
   base_attr   VARCHAR2(400),
   null_attr   INTEGER, -- Present only to demonstrate non-default constructors
   CONSTRUCTOR FUNCTION base_type
   (
      i_base_id INTEGER,
      i_base_attr VARCHAR2
   ) RETURN SELF AS RESULT,
   MEMBER FUNCTION get_base_id RETURN INTEGER,
   MEMBER FUNCTION get_base_attr RETURN VARCHAR2,
   MEMBER PROCEDURE set_base_id(i_base_id INTEGER),
   MEMBER PROCEDURE set_base_attr(i_base_attr VARCHAR2),
   MEMBER FUNCTION to_string RETURN VARCHAR2
) INSTANTIABLE NOT FINAL

Type body:

CREATE OR REPLACE TYPE BODY base_type AS
   CONSTRUCTOR FUNCTION base_type
   (
      i_base_id INTEGER,
      i_base_attr VARCHAR2
   ) RETURN SELF AS RESULT
   IS
   BEGIN
      self.base_id := i_base_id;
      self.base_attr := i_base_attr;
      RETURN;
   END base_type;

   MEMBER FUNCTION get_base_id RETURN INTEGER IS
   BEGIN
      RETURN self.base_id;
   END get_base_id;

   MEMBER FUNCTION get_base_attr RETURN VARCHAR2 IS
   BEGIN
      RETURN self.base_attr;
   END get_base_attr;

   MEMBER PROCEDURE set_base_id(i_base_id INTEGER) IS
   BEGIN
      self.base_id := i_base_id;
   END set_base_id;

   MEMBER PROCEDURE set_base_attr(i_base_attr VARCHAR2) IS
   BEGIN
      self.base_attr := i_base_attr;
   END set_base_attr;

   MEMBER FUNCTION to_string RETURN VARCHAR2 IS
   BEGIN
      RETURN 'BASE_ID ['||self.base_id||']; BASE_ATTR ['||self.base_attr||']';
   END to_string;
END;

MID_TYPE

Type declaration:

CREATE OR REPLACE TYPE mid_type UNDER base_type
(
   mid_attr DATE,
   CONSTRUCTOR FUNCTION mid_type
   (
      i_base_id   INTEGER,
      i_base_attr VARCHAR2,
      i_mid_attr  DATE
   ) RETURN SELF AS RESULT,
   MEMBER FUNCTION get_mid_attr RETURN DATE,
   MEMBER PROCEDURE set_mid_attr(i_mid_attr DATE),
   OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2
) INSTANTIABLE NOT FINAL

Type body:

CREATE OR REPLACE TYPE BODY mid_type AS
   CONSTRUCTOR FUNCTION mid_type
   (
      i_base_id   INTEGER,
      i_base_attr VARCHAR2,
      i_mid_attr  DATE
   ) RETURN SELF AS RESULT
   IS
   BEGIN
      self.base_id := i_base_id;
      self.base_attr := i_base_attr;
      self.mid_attr := i_mid_attr;
      RETURN;
   END mid_type;

   MEMBER FUNCTION get_mid_attr RETURN DATE IS
   BEGIN
      RETURN self.mid_attr;
   END get_mid_attr;

   MEMBER PROCEDURE set_mid_attr(i_mid_attr DATE) IS
   BEGIN
      self.mid_attr := i_mid_attr;
   END set_mid_attr;

   OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2
   IS
   BEGIN
      RETURN (SELF AS base_type).to_string || '; MID_ATTR [' || self.mid_attr || ']';
   END to_string;
END;

LEAF_TYPE

Type declaration:

CREATE OR REPLACE TYPE leaf_type UNDER mid_type
(
   leaf_attr VARCHAR2(1000),
   CONSTRUCTOR FUNCTION leaf_type
   (
      i_base_id   INTEGER,
      i_base_attr VARCHAR2,
      i_mid_attr  DATE,
      i_leaf_attr VARCHAR2
   ) RETURN SELF AS RESULT,
   MEMBER FUNCTION get_leaf_attr RETURN VARCHAR2,
   MEMBER PROCEDURE set_leaf_attr(i_leaf_attr VARCHAR2),
   OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2
) INSTANTIABLE FINAL

Type Body:

CREATE OR REPLACE TYPE BODY leaf_type AS
   CONSTRUCTOR FUNCTION leaf_type
   (
      i_base_id   INTEGER,
      i_base_attr VARCHAR2,
      i_mid_attr  DATE,
      i_leaf_attr VARCHAR2
   ) RETURN SELF AS RESULT
   IS
   BEGIN
      self.base_id := i_base_id;
      self.base_attr := i_base_attr;
      self.mid_attr := i_mid_attr;
      self.leaf_attr := i_leaf_attr;
      RETURN;
   END leaf_type;

   MEMBER FUNCTION get_leaf_attr RETURN VARCHAR2 IS
   BEGIN
      RETURN self.leaf_attr;
   END get_leaf_attr;

   MEMBER PROCEDURE set_leaf_attr(i_leaf_attr VARCHAR2) IS
   BEGIN
      self.leaf_attr := i_leaf_attr;
   END set_leaf_attr;

   OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2 IS
   BEGIN
      RETURN (SELF AS mid_type).to_string || '; LEAF_ATTR [' || self.leaf_attr || ']';
   END to_string;
END;

Accessing stored objects

CREATE SEQUENCE test_seq START WITH 1001;

CREATE TABLE test_tab
(
   test_id  INTEGER,
   test_obj base_type,
   PRIMARY KEY (test_id)
);

INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, base_type(1,'BASE_TYPE'));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, base_type(2,'BASE_TYPE'));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, mid_type(3, 'MID_TYPE',SYSDATE - 1));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, mid_type(4, 'MID_TYPE',SYSDATE + 1));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, leaf_type(5, 'LEAF_TYPE',SYSDATE - 20,'Maple'));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, leaf_type(6, 'LEAF_TYPE',SYSDATE + 20,'Oak'));

Returns object reference:

SELECT test_id
      ,test_obj
  FROM test_tab;

Returns object reference, pushing all to subtype

SELECT test_id
      ,TREAT(test_obj AS mid_type) AS obj
  FROM test_tab;

Returns a string descriptor of each object, by type

SELECT test_id
      ,TREAT(test_obj AS base_type).to_string() AS to_string -- Parenthesis are needed after the function name, or Oracle will look for an attribute of this name.
  FROM test_tab;