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Moving a Java Program into a Database

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Motivation

• We would like to be able to run a Java program from within Oracle. This will allow us to:– call a Java function inside a query– call a Java function inside a trigger (triggers will be

explained later on…)

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Basic Procedure

1. Create a Java program. Make the function that we want to use static.

2. Load the Java program into the database.

3. Create a PL/SQL procedure that will wrap the Java function

4. Call the PL/SQL procedure.

We learn each step in detail…

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Hello World - Java

CREATE OR REPLACE AND COMPILE JAVA SOURCE NAMED "Hello" ASpublic class Hello { public static void sayHello(String name) {      System.out.println("Hello World, " + name); } public static String returnHello(String name) { return "Hello World, " + name; }};/

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Hello World – PL/SQL (1)

CREATE OR REPLACE PROCEDURE say_hello(name VARCHAR2) as LANGUAGE JAVA NAME 'Hello.sayHello(java.lang.String)'; /

Note: Errors in creating a procedure can be seen with the command:

show errors

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Calling say_hello

SET SERVEROUTPUT ON SIZE 1000000CALL DBMS_JAVA.SET_OUTPUT (1000000);

CALL say_hello(‘Sara’);

We will see: “Hello World, Sara” on the screen.

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Hello World – PL/SQL

CREATE OR REPLACE FUNCTION return_hello(name VARCHAR2) return VARCHAR2 as LANGUAGE JAVA NAME 'Hello.returnHello(java.lang.String) return java.lang.String'; /

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Calling return_hello

SELECT return_hello(‘Sara’)FROM DUAL;

We will see:

RETURNHELLO('SARA')

----------------------------------

Hello World, Sara

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Notes

• Java programs can also be loaded using the utility loadjava. Details will be given when necessary.

• It may be necessary sometimes to recompile a procedure or a java source. This can be done by:– alter procedure say_hello compile;– alter java source “Hello” compile;

• Note the need to use quotes around Java source names, since Java is case sensitive.

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Moving Program Logic into the Database: Triggers

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What is a Trigger?

• A trigger is a procedure that is automatically called when certain events occur in the database.

• Triggers can be made to run when rows are inserted, deleted or updated.

• Triggers can be run before or after the action.• Triggers can be run once per statement or

once per row affected.

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General Form of a Trigger

CREATE [or REPLACE] TRIGGER trig_name

{BEFORE | AFTER | INSTEAD OF}

{DELETE | INSERT | UPDATE [of column [, column] ...] }

[or {DELETE | INSERT | UPDATE [of column [, column] ...] } ...]

on {table_name | view_name}

FOR EACH {ROW | STATEMENT} [WHEN (condition)]

PL/SQL block

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Backing Up Data

CREATE TRIGGER backup_sailors_trig

AFTER UPDATE of Rating

on Sailors

FOR EACH ROW WHEN (old.rating < new.rating)

BEGININSERT INTO Sailors_Backup VALUES (:old.sid, :old.sname, :old:age, :old:rating);

END/

Why AFTER?

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Ensuring Upper Case

CREATE TRIGGER upper_case_program_type_trig

BEFORE INSERT or UPDATE

on Program

FOR EACH ROW

BEGIN:new.type := UPPER(:new.type);

END/

Why BEFORE?

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Calling a Procedure

CREATE TRIGGER notify_ta_trig

AFTER INSERT or UPDATE or DELETE

on Db_Grades

FOR EACH STATEMENT WHEN(User <> ‘db’)

BEGIN call sendEmail(User || ‘ trying to access table Db_Grades’);END/

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Views and Triggers

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Changing a Table through a View (1)

• If a view is based on a single table you can insert, update and delete rows from the table through the view under the following conditions:– You can’t insert if the underlying table has non

null columns not appearing in the view– You can’t insert or update if any of the view

columns referenced in the command contains functions or calculations

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Changing a Table through a View (2)

– You can’t insert, update or delete if the view contains group by or distinct.

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Inserting Allowed

CREATE VIEW OldSailors asSELECT * FROM Sailors WHERE age > 50;

INSERT INTO OldSailors(sid,sname,age,rating) VALUES(12,‘Joe’,51,10);

INSERT INTO OldSailors(sid,sname,age,rating) VALUES(12,‘Mary’,49,10);

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Inserting Not Allowed

CREATE VIEW SailorsInfo asSELECT sname, ratingFROM SailorsWHERE age>50;

INSERT INTO SailorsInfo VALUES(‘Joe’,10);

Illegal!

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Updating Allowed

CREATE VIEW SailorsInfo asSELECT sname, ratingFROM SailorsWHERE age>50;

UPDATE SailorsInfo SET rating = 6WHERE sname = ‘Joe’;

UPDATE SailorsSET rating = 6WHERE sname = ‘Joe’ and age>50;

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Updating Not Allowed

CREATE VIEW SailorsInfo2 asSELECT sname, rating + age as raFROM SailorsWHERE age>50;

UPDATE SailorsInfo2 SET ra = 7WHERE sname = ‘Joe’; Illegal!

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Deleting Allowed

CREATE VIEW SailorsInfo2 asSELECT sname, rating + age as raFROM SailorsWHERE age>50;

DELETE FROM SailorsInfo2 WHERE sname = ‘Joe’

and ra = 56;

DELETE FROM SailorsWHERE sname = ‘Joe’ and

(rating + age) >50 and age > 50;

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Some More Examples:What will these commands do?UPDATE OldSailorsSET rating = 10;

DELETE FROM OldSailors;

UPDATE OldSailorsSET age = age +1 WHERE age <= 50;

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Using a Views with Triggers

Consider the relation:

All_Favorites(url, login)

This table stores the favorite web sites of CS students. Two views have been created over this table:• User_Favorites: The favorites of current user• Anon_Favorites: All the favorites, but without stud_id, to preserve anonymity.

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The Views

CREATE View User_Favorites asSELECT urlFROM All_FavoritesWHERE login = user;

CREATE View Anon_Favorites asSELECT urlFROM All_Favorites;

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Inserting New URLs

• The table All_Favorites can not be inserted into directly by a student because the privileges are lacking

• The views can’t be inserted through, since login is a non null column

CREATE TRIGGER insert_urlINSTEAD of INSERT on User_Favorites for each rowbegin

insert into All_Favorites(url, login)values(User,:new.url);

end;

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Using Triggers to Manipulate Complex Views

• Oracle can sometimes insert through a view based on several tables.

• Oracle can’t insert into multiple tables through a view.

CREATE VIEW SailorsReserves asSELECT S.sid, sname, rating, age, bid, dateFROM Sailors S, Reserves RWHERE S.sid = R.sid;

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Inserting into a Complex View:Won’t Work

• This won’t work, since we are attempting to insert into 2 tables.

• In addition, we are not specifying a value for the sid field of Reserves, which is part of the key!

INSERT INTO SailorsReserves(sid,sname,rating,age,bid,date)VALUES (1,’Joe’, 10, 50, 103, ’10-10-01’);

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Using a Trigger to Insert

CREATE TRIGGER insert_sailors_reserves_trigINSTEAD of INSERT on SailorsReserves for each rowbegin insert into Sailors(sid, sname, rating, age) values(:new.sid, :new.sname, :new.rating, :new.age);

insert into Reserves(sid, bid, date) values(:new.sid, :new.bid, :new.date);end;

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Materialized Views

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What and Why?

• What: A materialized view is a view that actually exists as a table

• Why: This can be more efficient than re-computing the view’s query each time it is accessed

• Problem: How is the materialized view kept up to date when the underlying tables are changed?

• Note: We will just see the ideas here and not the syntax

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Simple vs. Complex

A Simple Materialized View:1. Selects rows from only 1 table

2. Does not perform set operations, joins or group bys

Otherwise, it is a Complex Materialized View.

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Options for Materialized Views

• Refresh mode, one of– Fast (only possible for Simple Materialized Views):

add minimal changes– Complete: Recompute the query– Force: Fast, if possible; otherwise complete

• When is refresh performed?– On demand: When refresh is specifically asked for– On commit: When underlying table has changed

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Fast Refresh

• Consider a materialized view defined by the query:

SELECT sname, ageFROM Sailors WHERE rating < 10 and age > 50;

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Fast Refresh

INSERT INTO Sailors(sid,sname,rating,age)VALUES (12,’Joe’,8,52);

• How would the view be updated when the following commands are performed?

DELETE FROM SailorsWHERE age < 54;

UPDATE Sailors SET age = age - 1WHERE rating > 10;

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More Options

• Query Rewrite: Can a materialized view be used instead of a table in a query?

• Suppose we had the view defined before, and we wanted to compute the query:

SELECT ageFROM Sailors WHERE age > 51 and age < 85;