Question

CREATE TYPE person_typ AS OBJECT (
  idno           NUMBER,
  first_name     VARCHAR2(20),
  last_name      VARCHAR2(25),
  email          VARCHAR2(25),
  phone          VARCHAR2(20),
  MAP MEMBER FUNCTION get_idno RETURN NUMBER
);


CREATE TYPE BODY person_typ AS
  MAP MEMBER FUNCTION get_idno RETURN NUMBER IS
  BEGIN
    RETURN idno;
  END;
END;




CREATE TABLE contacts (
  contact         person_typ,
  contact_date    DATE );

INSERT INTO contacts 
VALUES 
(  person_typ (65, 'Verna', 'Mills', 'vmills@example.com', '1-650-555-0125'), '24 Jun 2003' );

然后，根据documentation 当需要调用方法get_idno()时，应该这样做：

SELECT c.contact.get_idno() FROM contacts c;

为什么这里需要使用别名？也就是说，为什么不这样做：

SELECT contacts.contact.get_idno() FROM contacts;

Answer 1

您可以将其与面向对象编程进行比较。

You need to create the instance of an object , before using any methods of it .

You can not directly call it by using  contacts

为什么在调用对象方法时需要使用别名？

1 个答案: