db4o-5.0-tutorial-java帮助

Welcome

db4o is the native Java, .NET and Mono open source object database.

This documentation and tutorial is intended to get you started with db4o and to be a reliable

companion while you develop with db4o. Before you start, please make sure that you have downloaded

db4o is available for Java, for .NET and for Mono. This tutorial was written for Java . The structure of

the other distributions may be considerably different, so please use the tutorial for the version that you

plan to experiment with first.

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Download Contents

The db4o Java distribution comes as one zip file, db4o-5.0-java.zip. When you unzip this file, you get

the following directory structure:

db4o-5.0/doc/tutorial/db4o-5.0-tutorial.pdf

The PDF version of the tutorial allows best fulltext search capabilities.

.

db4o-5.0/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 occasionaly.

PDF by iText, generated by Doctor, courtesy of db4objects Inc.

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

db4o-5.0-java1.1.jar

will run with most Java JDKs that supply JDK 1.1.x functionality such as reflection and Exception

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 (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

- choose db4o-*.jar in this folder

- hit OK twice

1.3. db4o Object Manager

db4o 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:

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- db4o ObjectManager for Windows IKVM (Java VM included)

- db4o ObjectManager for Windows no Java VM

- db4o ObjectManager for Linux

PDF by iText, generated by Doctor, courtesy of db4objects Inc.

1.4. API Overview

Do 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.

The com.db4o package contains almost all of the functionality you will commonly need when using

database file, start a server, or connect to an existing server. It also lets you configure the db4o

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

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