object databases

I'm in the middle of developing yet another persistence framework for a client, having done it a couple of times before. Each time I refine my ideas about how to do it. I must say that this book has a thorough examination of issues and certainly food for thought as well as answers to a couple of questions I've had.

However, I wouldn't say it's a complete design (which it doesn't claim to be). I still found myself picking and choosing which patterns to use as is, which to modify to my liking, and which to discard.

Also, I was left with the impression that the book didn't give enough coverage to handling collections of objects. The material is mostly geared toward working with a single object, which is understandable. I just think it would have been helpful to have more discussion about handling collections. For example, what should happen when you request to load an object, but the criteria you passed to the loading mechanism results in data for more than one object being retrieved from the database? Hand back the first object? Raise an exception? If it's covered in the book, I missed it.

Further, I would like to see more discussion about WHEN to refresh an object from the underlying database and when to save to the database. I always struggle with that timing issue. Having studied EJB, I like how entity beans keep your bean in synch with the underlying database. But the EJB container intercepts calls and makes those things happen. When coding the persistence layer myself, that's not an option. So, again, this is something I'd like to see some light shed on.

Overall, though, a great book if you're interested in reading up on persistence layer patterns.

I am in the process of writing a thesis proposal that utilizing JDBC and TableModeler to access various database platforms as a prototype.

While prototyping the model, I encountered a lot of consideration of what is the best approach for certain implementation (mainly on JDBC). While looking into a few of designing books, I found this Data Access Patterns book that fits into my research needs. I have read other book such as Designing Flexible Object Oriented System with UML and not able to apply the concept or see solution in it. It is simply a conceptual book. No practical examples at all.

Mr. Nock has explained the design patterns very clearly in each chapter by using JDBC as a media. The examples are very easy to understand as compared to Design Patterns Explained. I am not able to understand codes that implementing graphics in that book.

Mr. Nock addressed the pros and cons of the patterns. Many techie books do not even bother to talk about pros and cons.

The author has chosen the right title for the book, I realized that many times author received a poor rating because reader expect different contents based on the title of the book.

The feature I liked the most - the ˇ§Applicabilityˇ¨ section on each chapter. Unlike other patterns book, the author explains the concept and gives example of "what" and "when" to use certain design pattern. This section is pretty much the answer for my thesis obstacles. The answer is in this book!!

Minor typos do exist such as in page 390 roll back instead of rollback.

In concurrency chapter, author may have mis-used the term of updates locking. It should be Lost Updates instead of Missing updates. Concurrency chapter looks like UDB Lock Concurrency architecture.

Additional note - would like to see the quality aspect in each of the patterns.

Overall, the book is very well structured, explained and thoughtful.

Thank you Mr. Nock !! This is a perfect book for my thesis.

Looking forward to read your future publish.

Regards,

EQ

I have to disagree with the previous review. I will try to explain why I think 'b88zhou' review is inadequate after presenting my overview of this book.

After reading numerous pattern books, it is nice to see a pattern book with very good organization.

Each pattern is presented with the following subsections.

* Description
* Context
* Applicability
* Structure
* Iteractions
* Consequences
* Strategies
* Sample Code
* Related Patterns and Technology.

I specifically like 'Consequence' section because it outlines the 'bad' consequence of adopting the patter. This goes with the mantra of design patterns - there is no one good pattern. You trade off one design for another depending on the context of your domain.

Also each pattern is accompanied by UML class diagrams and UML sequence diagrams - this is a big plus in understanding pattern.

The sample code is written in Java/JDBC so you may need to understand Java but I believe this pattern is still relevant to ADO.NET and C++. [ ADO.Net does offer connected and disconnected database operation so some patterns may not be relevant - plus, event/delegate will aid in some patterns.]

Specific to what the previous reviewer say - here are my rebuttals.

>> Why do you want to make queries and database updates into factories? Looking at the sample code, does it really help decoupling?

The previous reviewer mentioned as 'factories' is the derivation of 'AbstractFactory'. If you do not understand why AbstractFactory aids in decoupling from the concrete implementation, I think you should re-read GoF book. The author uses AbstractFactory pattern extensively in context of "Input and Output Parameter" and "Cache Patterns". I do admit that sometimes "Input and Output Parameter patterns" may not need to use AbstractFactory but if you read 'Domain Assembler' pattern you will understand why. From Domain Assembler, you can see the benefit of having AbstractFactories for Selection, Domain Object, and Update -- assembling all these factories via interface not concrete implmentation - a basic idea of design to interface instead concrete implementation.

>> The "Cache Patterns" does not solve the problem of preventing stale entry or even attempt to describe how to invalidate cache entry, so no matter how efficient you get, the cache is not guaranteed to be up-to-date /correct.

Please re-read 'Cache Collector'. The pattern could have different name like 'Cache Garbage Collector'. He talks about how you can 'purge' old data. Also re-read 'Cache Replicator' for how to sync the cached data in distributed system.

>> I'm surprised "stored procedure" is not mentioned at all.

I guess you have not done too many DB oriented projects. The stored procedure is evil and add little value to OO programming. But if you want the stored procedure, just replace 'SELECT' or 'UPDATE' statements to whatever stored procedures you want to call. So I don't think you can add much with SP.

>> mature object/relational frameworks like EOF (Apple WebObjects) or TopLink

This book is not about Java Data Object or OR mapping. Object-Relational mapping tool is another beast.

I would recommend this book highly to anyone doing DB application development.