MID TYPE

类型声明：

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

输入体型：

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;