Download IT Boxing Championship

Svetoslav Kapralov
Contents
1. DB4O Overview
• OODBMS vs. RDBMS
• What is DB4O
2. DB4O Basics
• Object Container
• CRUD
• Activation
• Transactions
DB4O Overview
OОDBMS (db4o) vs. RDBMS
• Object-oriented programming (OOP) and
relational databases (RDBMS) do not match up
• An object database (ODBMS) stores objects
directly
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 faster than Hibernate +
RDBMS!
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
DB4O Basics
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
Storing Objects
• Objects stored using method set of
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);
Retrieving Objects
• db4o supports three query languages
• QBE
• Native query
• SODA
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());
}
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>() {
public boolean match(Book book) {
return book.getYear() > 1995;
}
}
);
for (Book book: books) {
System.out.println(book.getTitle());
}
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 set method
• Delete procedure for persistent object
• retrieve desired object from the database
• method delete of ObjectContainer removes
objects
CRUD Summary
• Storing of new objects using the set method
• object graph is traversed and all
referenced objects are stored
• Updating of existing objects using the set
method
• by default update depth is set to one
• only primitive and string values are
updated
• object graph is not traversed for reasons
of performance
CRUD Summary
• Deleting existing objects using the delete
method
• by default delete operations are not
cascaded
• referenced objects have to be deleted
manually
• cascading delete can be configured for
individual classes
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
Activation
• Activation depth trade-off
• set to maximum
• set to minimum
• Controlling activation
• default activation depth is 5
• methods activate and deactivate of
ObjectContainer
• per class configuration
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