1. First GlanceBefore 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-5.0/lib/.db4o-5.0-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-5.0-java1.2.jar is built for all Java JDKs between 1.2 and 1.4. db4o-5.0-java5.jar is built for Java JDK 5. 1.2. InstallationIf 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 (We really recommend Eclipse, it's also free.) you would copy the db4o-*.jar to a /lib/ folder under your project and add db4o to your project as a library. (You only need to copy the one jar file for the distribution you are targeting.)Here is how to add the db4o library to an Eclipse project - create a folder named "lib" under your project directory, if it doesn't exist yet - copy db4o-*.jar to this folder - Right-click on your project in the Package Explorer and choose "refresh" - Right-click on your project in the Package Explorer again and choose "properties" - select "Java Build Path" in the treeview on the left - select the "Libraries" tabpage. - click "Add Jar" - the "lib" folder should appear below your project - choose db4o-*.jar in this folder - hit OK twice 1.3. db4o Object Managerdb4o Object Manager is a GUI tool to browse and query the contents of any db4o database file. Object Manager has to be downloaded seperately from the main db4o distributions. Please visit the db4o Download Center and choose the installation appropriate for your system. The following distributions are currently available: - db4o ObjectManager for Windows IKVM (Java VM included) - db4o ObjectManager for Windows no Java VM - db4o ObjectManager for Linux 1.4. API OverviewDo not forget the API documentation while reading through this tutorial. It provides an organized view of the API, looking from a package perspective and you may find related functionality to the theme you are currently reading up on.For starters, the packages com.db4o and com.db4o.query are all that you need to worry about. com.db4o The com.db4o 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 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 to get to the advanced features. com.db4o.config The com.db4o.config package contains types and classes necessary to configure db4o. The objects and interfaces within are discussed in the Configuration section. com.db4o.query The com.db4o.query package contains the Predicate class to construct Native Queries. The Native Query interface is the primary db4o querying interface and should be preferred over the Query API. -- generated by Doctor courtesy of db4objects Inc. |