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Bemerkungen
Es ist wichtig zu beachten, dass ein Objektkörper nicht immer notwendig ist. Wenn der Standardkonstruktor ausreicht und keine andere Funktionalität implementiert werden muss, sollte er nicht erstellt werden.
Ein Standardkonstruktor ist der von Oracle gelieferte Konstruktor, der aus allen in Deklarationsreihenfolge aufgelisteten Attributen besteht. Eine Instanz von BASE_TYPE könnte beispielsweise durch den folgenden Aufruf erstellt werden, obwohl wir sie nicht explizit deklarieren.
l_obj := BASE_TYPE(1, 'Default', 1);
BASISTYP
Typdeklaration:
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
Typ Körper:
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
Typdeklaration:
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
Typ Körper:
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
Typdeklaration:
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
Typ Körper:
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;
Zugriff auf gespeicherte Objekte
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'));
Gibt eine Objektreferenz zurück:
SELECT test_id
,test_obj
FROM test_tab;
Gibt die Objektreferenz zurück und drückt alle auf den Untertyp
SELECT test_id
,TREAT(test_obj AS mid_type) AS obj
FROM test_tab;
Gibt einen String-Deskriptor für jedes Objekt nach Typ zurück
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;
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