lab2.sql

-- description

-- в базе для стоянки (парковки) существует 2 таблицы (garage и car_change), 
-- предназначенные для слежки за парковочными местами (гаражами).
-- при въезде одного и того же владельца в тот же самый гараж проверяется
-- какой автомобиль до этого стоял в нем (гараже).
-- в случае отличия номеров автомобилей создается новая запись в таблице car_change

-- table creations

create table garage (
  id NUMBER(10) NOT NULL,
  garage_id NUMBER(10) NOT NULL,
  user_id NUMBER(10) NOT NULL,
  car_id NUMBER(10) NOT NULL,
  created_at DATE DEFAULT SYSDATE,
  CONSTRAINT pk_member PRIMARY KEY (id)
);

create table car_change (
  id NUMBER(10) NOT NULL,
  garage_id NUMBER(10) NOT NULL,
  user_id NUMBER(10) NOT NULL,
  old_car_id NUMBER(10) NOT NULL,
  new_car_id NUMBER(10),
  created_at DATE DEFAULT SYSDATE,
  CONSTRAINT pk_car_change PRIMARY KEY (id)
);


-- sequences

CREATE sequence garage_seq start WITH 1 increment BY 1;
CREATE sequence car_change_seq start WITH 1 increment BY 1;

CREATE OR REPLACE TRIGGER garage_set_id
BEFORE INSERT ON garage FOR each row
BEGIN
  IF :new.id IS NULL THEN
    SELECT garage_seq.NEXTVAL
    INTO :new.id
    FROM dual;
  END IF;
END;
/
CREATE OR REPLACE TRIGGER car_change_set_id
BEFORE INSERT ON car_change FOR each row
BEGIN
  IF :new.id IS NULL THEN
    SELECT car_change_seq.NEXTVAL
    INTO :new.id
    FROM dual;
  END IF;
END;
/

-- package

CREATE OR REPLACE PACKAGE garage_package AS
  type       rArray IS TABLE OF NUMBER INDEX BY BINARY_INTEGER;
  ids        rArray;
  locked     NUMBER;
  cnt        NUMBER;
  now_locked EXCEPTION;

  PROCEDURE lock_package;
  PROCEDURE unlock_package;
  PROCEDURE collect (
    gar_id garage.id%TYPE
  );
  PROCEDURE process;
END;
/
CREATE OR REPLACE PACKAGE BODY garage_package AS
  PROCEDURE lock_package IS
  BEGIN
    cnt := 0;

    IF locked = 1 THEN
      RAISE now_locked;
    ELSE
      locked := 1;
    END IF;

    EXCEPTION
      WHEN now_locked THEN
        unlock_package;
        RAISE_APPLICATION_ERROR(-20000, 'Can not write! Please wait');
  END;

  PROCEDURE unlock_package IS
  BEGIN
    locked := 0;
  END;

  PROCEDURE collect (
    gar_id garage.id%TYPE
  ) IS
  BEGIN
    cnt := cnt + 1;
    ids(cnt) := gar_id;
  END;

  PROCEDURE process IS
    old_car garage.car_id%TYPE;
    rec     garage%rowtype;
  BEGIN
    FOR i IN 1 .. cnt LOOP
    BEGIN
      SELECT * INTO rec FROM garage WHERE id = ids(i);

      SELECT   car_id INTO old_car
      FROM     garage
      WHERE    id < rec.id AND user_id = rec.user_id AND garage_id = rec.garage_id AND rownum = 1
      ORDER BY id DESC;

      IF old_car > 0 AND old_car <> rec.car_id THEN
        INSERT INTO car_change (garage_id, user_id, old_car_id, new_car_id) VALUES (rec.garage_id, rec.user_id, old_car, rec.car_id);
      END IF;
    END;
    END LOOP;

    cnt := 0;

    EXCEPTION
      WHEN NO_DATA_FOUND THEN
        unlock_package;
        NULL;
      WHEN OTHERS THEN
        unlock_package;
        DBMS_OUTPUT.PUT_LINE(SQLERRM);
  END;
END;
/


-- triggers

CREATE OR REPLACE TRIGGER garage_lock
BEFORE INSERT ON garage
BEGIN
  garage_package.lock_package;
END;
/
CREATE OR REPLACE TRIGGER garage_after_row
AFTER INSERT ON garage FOR each row
BEGIN
  garage_package.collect(:new.id);
END;
/
CREATE OR REPLACE TRIGGER garage_process
AFTER INSERT ON garage
BEGIN
  garage_package.process;
  garage_package.unlock_package;
END;
/

-- disable package related triggers
-- alter trigger garage_lock disable;
-- alter trigger garage_after_row disable;
-- alter trigger garage_process disable;

-- autonomous transaction

CREATE OR REPLACE TRIGGER garage_bi_trans
AFTER INSERT ON garage FOR EACH ROW
DECLARE
  old_car NUMBER(10);
  PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
  SELECT    car_id INTO old_car
  FROM      garage
  WHERE     garage_id = :new.garage_id
        AND user_id = :new.user_id
        AND car_id <> :new.car_id
        AND rownum = 1
  ORDER BY  id DESC;

  IF old_car > 0 THEN
    INSERT INTO car_change (garage_id, user_id, old_car_id, new_car_id) VALUES (:new.garage_id, :new.user_id, old_car, :new.car_id);
    COMMIT;
  END IF;

  EXCEPTION
    WHEN NO_DATA_FOUND THEN
      NULL;
    WHEN OTHERS THEN
      DBMS_OUTPUT.PUT_LINE(SQLERRM);
END;
/

-- temporarily disable autonomous transaction trigger
alter trigger garage_bi_trans disable;

-- example queries

insert into garage (garage_id, user_id, car_id) values (1,1,1);
insert into garage (garage_id, user_id, car_id) values (1,1,1);
insert into garage (garage_id, user_id, car_id) values (1,2,1);
insert into garage (garage_id, user_id, car_id) values (1,1,2);
insert into garage (garage_id, user_id, car_id) (select 1,1,2 from dual union select 1,1,3 from dual union select 1,1,3 from dual union select 1,1,4 from dual);