Методы сравнения для типов объектов, часть 5

Обратите внимание, что я использую ключевое слово ORDER, передаю экземпляр типа, с которым сравнивается SELF. Я возвращаю целое число: либо -1, 0 или 1. А теперь реализация. Вот некоторые примечания, учитывая их сложность:

• Поскольку экземпляром может быть еда, десерт или торт, первое правило заключается в том, что супертип всегда больше, чем подтип. Я использую синтаксис self IS OF (ONLY my_type) для определения типа экземпляра.
• Я использую коллекцию с индексами строк l_order_by_food_group, чтобы установить иерархию упорядочения по группам продуктов. (Мне действительно нравятся коллекции с индексами строк!)
• If after checking for supertype/subtype ordering, I know that other_food_in is of the same type as SELF, then I set return value according to food group.

CREATE OR REPLACE TYPE BODY food_ot
IS
   ORDER MEMBER FUNCTION food_ordering (other_food_in IN food_ot)
      RETURN INTEGER
   /*
   Subtypes are always less. Food > Dessert > Cake

   If of the same type, same rule AS for MAP:
      Vegetable < Carbohydrate < Liquid < Protein
   */
   IS
      TYPE order_by_food_group_t IS TABLE OF PLS_INTEGER
         INDEX BY VARCHAR2 (100);

      l_order_by_food_group   order_by_food_group_t;
      c_self_eq_of   CONSTANT PLS_INTEGER := 0;
      c_self_gt_of   CONSTANT PLS_INTEGER := 1;
      c_of_gt_self   CONSTANT PLS_INTEGER := -1;
      l_ordering              PLS_INTEGER := c_self_eq_of;

      PROCEDURE initialize
      IS
      BEGIN
         l_order_by_food_group ('PROTEIN') := 1000;
         l_order_by_food_group ('LIQUID') := 100;
         l_order_by_food_group ('CARBOHYDRATE') := 10;
         l_order_by_food_group ('VEGETABLE') := 1;
      END initialize;
   BEGIN
      initialize;

      IF self IS OF (ONLY food_ot)
      THEN
         l_ordering :=
            CASE
               WHEN other_food_in IS OF (ONLY food_ot) THEN c_self_eq_of
               ELSE c_self_gt_of
            END;
      ELSIF self IS OF (ONLY dessert_t)
      THEN
         l_ordering :=
            CASE
               WHEN other_food_in IS OF (ONLY dessert_t) THEN c_self_eq_of
               WHEN other_food_in IS OF (ONLY food_ot) THEN c_of_gt_self
               ELSE c_self_gt_of
            END;
      ELSE
         /* It is cake. */
         l_ordering :=
            CASE
               WHEN other_food_in IS OF (ONLY cake_t) THEN c_self_eq_of
               ELSE c_of_gt_self
            END;
      END IF;

      IF l_ordering = c_self_eq_of
      THEN
         /*
         Further analysis is needed.
         */
         l_ordering :=
            CASE
               WHEN l_order_by_food_group (self.food_group) =
                       l_order_by_food_group (other_food_in.food_group)
               THEN
                  c_self_eq_of
               WHEN l_order_by_food_group (self.food_group) >
                       l_order_by_food_group (other_food_in.food_group)
               THEN
                  c_self_gt_of
               WHEN l_order_by_food_group (self.food_group) <
                       l_order_by_food_group (other_food_in.food_group)
               THEN
                  c_of_gt_self
            END;
      END IF;

      RETURN l_ordering;
   END;
END;
/

BEGIN
   -- Populate the meal table
   INSERT INTO meals
        VALUES (SYSDATE, food_ot ('Shrimp cocktail', 'PROTEIN'));

   INSERT INTO meals
        VALUES (SYSDATE + 1, food_ot ('Stir fry tofu', 'PROTEIN'));

   INSERT INTO meals
        VALUES (SYSDATE + 1,
                dessert_ot ('Peanut Butter Sandwich',
                            'CARBOHYDRATE',
                            'N',
                            1700));

   INSERT INTO meals
        VALUES (SYSDATE + 1, food_ot ('Brussels Sprouts', 'VEGETABLE'));

   INSERT INTO meals
        VALUES (SYSDATE + 1,
                cake_ot ('Carrot Cake',
                         'VEGETABLE',
                         'N',
                         1550,
                         12,
                         'Happy Birthday!'));

   COMMIT;
END;
/

  SELECT m.main_course.name name
  FROM meals m
ORDER BY main_course
/

NAME
----------------------
Carrot Cake
Peanut Butter Sandwich
Brussels Sprouts
Shrimp cocktail
Stir fry tofu

  SELECT m1.main_course.name name
    FROM (SELECT *
            FROM meals m
           WHERE m.main_course.name LIKE 'S%') m1,
         (SELECT *
            FROM meals m
           WHERE m.main_course.name NOT LIKE 'S%') m2
   WHERE m1.main_course > m2.main_course
ORDER BY m1.main_course
/

NAME
---------------
Shrimp cocktail
Shrimp cocktail
Shrimp cocktail
Stir fry tofu
Stir fry tofu
Stir fry tofu

DECLARE
   ot1   food_ot := food_ot ('Eggs benedict', 'PROTEIN');
   ot2   food_ot := food_ot ('Brussels Sprouts', 'VEGETABLE');
   ot3   food_ot := dessert_ot ('Brownie', 'SUGAR', 'Y', 1943);
   ot4   food_ot := cake_ot (
      'Carrot Cake', 'VEGETABLE', 'N', 1550, 12, 'Happy Birthday!');
BEGIN
   IF ot1 = ot1
   THEN
      DBMS_OUTPUT.put_line ('equal - correct');
   ELSE
      DBMS_OUTPUT.put_line ('not equal - incorrect');
   END IF;

   IF ot1 = ot2
   THEN
      DBMS_OUTPUT.put_line ('equal - incorrect');
   ELSE
      DBMS_OUTPUT.put_line ('not equal - correct');
   END IF;

   IF ot2 <> ot3
   THEN
      DBMS_OUTPUT.put_line ('not equal - correct');
   ELSE
      DBMS_OUTPUT.put_line ('equal - incorrect');
   END IF;

   IF ot2 > ot3
   THEN
      DBMS_OUTPUT.put_line ('food > dessert - correct');
   ELSE
      DBMS_OUTPUT.put_line ('food < dessert - incorrect');
   END IF;

   IF ot3 > ot4
   THEN
      DBMS_OUTPUT.put_line ('dessert > cake - correct');
   ELSE
      DBMS_OUTPUT.put_line ('dessert < cake - incorrect');
   END IF;

   IF ot3 < ot4
   THEN
      DBMS_OUTPUT.put_line ('dessert < cake - incorrect');
   ELSE
      DBMS_OUTPUT.put_line ('dessert > cake - correct');
   END IF;
END;
/

equal - correct
not equal - correct
not equal - correct
food > dessert - correct
dessert > cake - correct
dessert > cake - correct