Svetoslav Kapralov

1. Svetoslav Kapralov

2. Contents • DB4O Overview • OODBMS vs. RDBMS • What is DB4O • DB4O Basics • Object Container • CRUD • Activation • Transactions

3. DB4O Overview

4. OОDBMS (db4o) vs. RDBMS • Object-oriented programming (OOP) and relational databases (RDBMS) do not match up • An object database (ODBMS) stores objects directly

5. What is db4o? • Open source object database • Designed for embedded • 1,000,000 downloads, • 20,000 registered community members • 200 customers • Dual license model (GPL / commercial) • db4o is up to 55x fasterthan Hibernate + RDBMS!

6. What is db4o? • No Database Administrator required • No conversion or mapping needed since objects are stored as they are • Only one line of code to store objects of any complexity natively • Installation by adding a single library file

7. DB4O Basics

8. Object Container • Represents db4o databases • Supports local file mode or client connections to db4o server • All operations are executed transactional • Maintains references to stored and instantiated objects

9. Storing Objects • Objects stored using method setof ObjectContainer • Stores objects of arbitrary complexity ObjectContainer database = Db4o.openFile("test.db"); // create a publication Book book =new Book(“db4o"); // create authors Author lambo = new Author(“Lambo"); Author gruiu = new Author(“Gruiu"); // assign authors to book book.addAuthor(lambo); book.addAuthor(gruiu); //store complex object database.set(book);

10. Retrieving Objects • db4o supports three query languages • QBE • Native query • SODA

11. Query by Example • simple method based on prototype objects ObjectContainer database = Db4o.openFile("test.db"); // get author “Lambo" Author proto = new Author(“Lambo"); ObjectSet<Author> authors = database.get(proto); for (Author author: authors) { System.out.println(author.getName()); } // get all books ObjectSet<Book> books = database.get(Book.class); for (Book book: books) { System.out.println(book.getTitle()); }

12. Native Queries • type safe • transformed to SODA and optimized ObjectContainer database = Db4o.openFile("test.db"); // find all books after 1995 ObjectSet<Book> books = database.query( new Predicate<Book>() { publicboolean match(Book book) { return book.getYear() > 1995; } } ); for (Book book: books) { System.out.println(book.getTitle()); }

13. Update / Delete Objects • Update procedure for persistent object • retrieve desired object from the database • perform the required changes and modification • store object back to the database by calling the setmethod • Delete procedure for persistent object • retrieve desired object from the database • method deleteof ObjectContainerremoves objects

14. CRUD Summary • Storing of new objects using the setmethod • object graph is traversed and all referenced objects are stored • Updating of existing objects using the setmethod • by default update depth is set to one • only primitive and string values are updated • object graph is not traversed for reasons of performance

15. CRUD Summary • Deleting existing objects using the deletemethod • by default delete operations are not cascaded • referenced objects have to be deleted manually • cascading delete can be configured for individual classes

16. Activation • Activation controls instantiation of object fields • object field values are loaded into memory only to a certain depth when a query retrieves objects • activation depth denotes the length of the reference chain from an object to another • fields beyond the activation depth are set to null for object references or to default values for primitive types

17. Activation • Activation depth trade-off • set to maximum • set to minimum • Controlling activation • default activation depth is 5 • methods activateand deactivateof ObjectContainer • per class configuration

18. Transactions • ACID transaction model • Data transaction journaling • zero data loss in case of system failure • automatic data recovery after system failure • db4o core is thread-safe for simultaneous operations • db4o uses the read committed isolation level