Reader java1dev submits the following brief review of O'Reilly's Java Data Objects, which he says provides excellent coverage of JDO. His capsule description of the book: "First, a high-level overview, followed by an in-depth coverage of the core features, and concluding by describing the more complex concepts in detail. Running throughout the book is an excellent intuitive example application that illustrates the features being covered." Read on for more of his review.
Craig Russell, at Sun Microsystems, is the specification lead for JDO and David Jordan, at Object Identity, has been an active member of the JDO expert group since its inception.
Java Data Objects provides a thorough coverage of JDO and explains how it can be used in various architectures. The reader is expected to be familiar with Java but needs only a limited knowledge of databases. In brief, Java Data Objects (JDO) insulates you from needing to know a lot about databases. JDO permits you to develop applications using your preferred Java object-oriented model, without you having to write code to translate between Java objects and how the data is stored in the database--JDO takes care of all of that for you.
The first three chapters provide a high level overview of JDO by walking through a small application, exploring each of its interfaces at a high level, and introducing the architectures it might be used in. Even if you have been away from code for a while you will be able to follow most of the code example. You can stop here if you just want to understand what JDO is all about and where it can be used. These are recommended reading for a manager.
Chapters 4 through 9 are required reading if you want to start developing JDO applications. They really get you into JDO, so you can understand it and start using it. The first three of these cover how to define persistent classes and fields, how they can be mapped to various databases (done for you) and the class enhancement process (which makes a lot of JDO transparent to you). The next three (chapter 7 through 9) bring home the power of JDO. These cover how to connect with a database, establish a transaction context and create, read, query, update and delete database objects. The material is made concrete by illustrating it with a detailed and intuitive example application. This example is carried throughout the book with sections of it explained as the concepts are covered.
Each remaining chapter covers a different JDO concept or feature (including optional features) that were introduced earlier but not covered in detail to keep the earlier chapters more understandable. These remaining topics are identity, lifecycle states & transitions, field management, cache management, nontransactional access and optimistic transactions. You can read these chapters as you feel the need for a more in-depth understanding of these concepts.
The last two chapters explain how to use JDO in an application-server environment and an Enterprise Java Beans environment. These two chapters assume you are already familiar with these environments, but I think a lot of it is understandable even if you are not.
There are five appendices with everything from the lifecycle state transitions to the collected source code for many of the classes used in the example application.
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