Welcome
db4o is the native Java, .NET and Mono open source object database.
This tutorial was written to get you started with db4o as quickly as possible. Before you start, please
make sure that you have downloaded the latest db4o distribution from the db4objects website.
developer.db4o.com
You are invited to join the db4o community in the public db4o forums to ask for help at any time.
Please also try out the keyword search functionality on the db4o knowledgebase.
Links
Here are some further links on developer.db4o.com that you may find useful:
All Downloads
Release Note Blog
SVN Access
Design Wiki
Community Projects
www.db4o.com
Download Contents
The db4o Java distribution comes as one zip file, db4o-6.4-java.zip. When you unzip this file, you get
the following directory structure:
Please take a look at all the supplied documentation formats to choose the one that works best for
you:
.
db4o-6.4/doc/api/index.html
The API documentation for db4o is supplied as JavaDocs HTML files. While you read through this
tutorial it may be helpful to look into the API documentation occasionally.
db4o-6.4/doc/reference/index.html
www.db4o.com
The reference documentation is a complete compilation for experienced db4o users. It is maintained
online.
db4o-6.4/doc/tutorial/index.html
This is the interactive HTML tutorial. Examples can be run "live" against a db4o database from within
the browser. In order to use the interactive functionality a Java JRE 1.3 or above needs to be installed
and integrated into the browser. Java security settings have to allow applets to be run. If you have
problems using the interactive functionality, please refer to Tutorial Troubleshooting.
db4o-6.4/doc/tutorial/db4o-6.4-tutorial.pdf
The PDF version of the tutorial allows best fulltext search capabilities.
www.db4o.com
1. First Glance
Before diving straight into the first source code samples let's get you familiar with some basics.
1.1. The db4o engine
The db4o object database engine consists of one single jar file. This is all that you need to program
against. The versions supplied with the distribution can be found in /db4o-6.4/lib/. You will only need
one of the following libraries, not all of them.
db4o-6.4-java1.1.jar
will run with most Java JDKs that supply JDK 1.1.x functionality such as reflection and Exception
handling. That includes many IBM J9 configurations, Symbian and Savaje.
db4o-6.4-java1.2.jar
is built for all Java JDKs between 1.2 and 1.4.
db4o-6.4-java5.jar
is built for Java JDK 5.
1.2. Installation
If you add one of the above db4o-*.jar files to your CLASSPATH db4o is installed. In case you work
with an integrated development environment like Eclipse you would copy the db4o-*.jar to the /lib/
folder under your project and add db4o to your project as a library.
www.db4o.com
1.3. API Overview
Do not forget the API documentation while reading through this tutorial. It provides an organized view
of the API, looking from a java package perspective and you may find related functionality to the
theme you are currently reading up on.
For starters, the java packages com.db4o and com.db4o.query are all that you need to worry about.
com.db4o
The com.db4o java package contains almost all of the functionality you will commonly need when using
db4o. Two objects of note are com.db4o.Db4o, and the com.db4o.ObjectContainer interface.
The com.db4o.Db4o factory is your starting point. Static methods in this class allow you to open a
database file, start a server, or connect to an existing server. It also lets you configure the db4o
environment before opening a database.
The most important interface, and the one that you will be using 99% of the time is
com.db4o.ObjectContainer: This is your db4o database.
- An ObjectContainer can either be a database in single-user mode or a client connection to a db4o
server.
- Every ObjectContainer owns one transaction. All work is transactional. When you open an
ObjectContainer, you are in a transaction, when you commit() or rollback(), the next transaction is
started immediately.
- Every ObjectContainer maintains it's own references to stored and instantiated objects. In doing so, it
manages object identities, and is able to achieve a high level of performance.
- ObjectContainers are intended to be kept open as long as you work against them. When you close an
ObjectContainer, all database references to objects in RAM will be discarded.
com.db4o.ext
In case you wonder why you only see very few methods in an ObjectContainer, here is why: The db4o
interface is supplied in two steps in two java packages, com.db4o and com.db4o.ext for the following
reasons:
- It's easier to get started, because the important methods are emphasized.
- It will be easier for other products to copy the basic db4o interface.
- It is an example of how a lightweight version of db4o could look.
Every com.db4o.ObjectContainer object is also an com.db4o.ext.ExtObjectContainer. You can cast it to
ExtObjectContainer or you can use the method to get to the advanced features.
com.db4o.config
