IT Boxing Championship

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Svetoslav Kapralov
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Contents

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

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DB4O Overview
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O?DBMS (db4o) vs. RDBMS

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

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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!

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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

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DB4O Basics
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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

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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)
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Retrieving Objects

• db4o supports three query languages
• QBE
• Native query
• SODA

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Query by Example

• simple method based on prototype objects

ObjectContainer database Db4o.openFile("test.db"
) // get author Lambo" Author proto new
Author(Lambo") ObjectSetltAuthorgt authors
database.get(proto) for (Author author authors)
System.out.println(author.getName()) // get
all books ObjectSetltBookgt books
database.get(Book.class) for (Book book books)
System.out.println(book.getTitle())
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Native Queries

• type safe
• transformed to SODA and optimized

ObjectContainer database Db4o.openFile("test.db"
) // find all books after 1995 ObjectSetltBookgt
books database.query( new PredicateltBookgt()
public boolean match(Book book) return
book.getYear() gt 1995 ) for (Book book
books) System.out.println(book.getTitle())
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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

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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

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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

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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

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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

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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