Rating: 
Summary: Excellent, Solid, JDO Book
Review: This is a solid and very readable treatment of the JDO specification. The authors are well qualified: Craig Russell was the specification lead and David Jordan a key contributor to the expert group. They have both been involved in persistence for many years. Craig Russell is one of the authors of the JDO implementation used in the SunONE application server to implement EJB CMP.The first chapter helps to get the user started with the JDO reference implementation. In just 27 pages all the basic persistence operations are covered in the context of a simple demo application. This chapter provides enough information to get started with JDO on a project. However I would recommend using an evaluation download of one of the commercial JDO implementations or an open source JDO implementation instead of the reference implementation. The reference implementation uses a file system store and most users will want to use JDO with a relational database. Chapter 2 covers the JDO API with a short informative description of each class and interface. Chapter 3 describes different JDO architectures. This chapter is missing the "remote persistence manager" architecture supported by some JDO implementations (JDO Genie and Object Frontier). Otherwise it is complete and has very clear diagrams. Chapter 4 covers the definition of JDO meta data. Chapter 5 covers Object / Relational mapping with JDO. The JDO specification does not define any mappings (relational database mapping will be in JDO 2.0 as JDO/R) however most JDO implementations work with relational databases. The information is applicable to all O/R mapping JDO implementations as they all map in very similar ways. Forward engineering (write classes first), reverse engineering (generate classes from tables) and bridge mapping (write classes and design tables and map them together) are well explained. Chapter 6 explains how JDO byte code enhancement works. Chapter 9 is a detailed explanation of the JDO query language (JDOQL). Chapter 10 covers the different types of identity supported by JDO. Tricky topics such as compound primary keys including references to other classes are very clearly explained. The chapter titled "Web Server Environment" (16) is a bit thin on some details. For example it does not discuss giving the view (e.g. JSP pages) managed JDO instances to render. This is a very useful technique available to web applications and should have been covered. The balance of the chapters cover more advanced topics such as state transitions, local cache management, transactions, J2EE integration, field management, non-transactional access and optimistic transactions. This book succeeds in making JDO easy to understand and learn by deferring detail on complex topics to later chapters. Advanced users can read the whole book for a comprehensive understanding of the specification. I strongly recommend this book for anyone who is using or thinking about using JDO.
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