Through the years I’ve encountered a recurring requirement. Clients need to log changes to the database for auditing and legal purposes. To satisfy this requirement you could add logging to every save/update/delete call in your code. Or better yet, you could create an aspect that wraps these calls. While these would certainly work Hibernate provides a convenient interceptor.
In this article I will show you how to add a simple logger to Hibernate.
Lately I have been thinking that the standard service-calling-the-dao-layer architecture hasn’t been working out as well as I would hope. The applications I have been working on have been using Spring and Hibernate with a dao object per model object. While this does provide a good separation between the two, I have been finding it increasingly difficult to write good tests for the service layer as the project matures. Past experience has shown that if writing tests is difficult, then it just isn’t done. Follow along as I think about possible ways to address this issue.
Well this turned out to be quite an exercise.
The goal: scalable reads with MySQL in master-slave configuration, writing to the master, and reading from N slaves, load balanced in round-robin fashion (or something).
The problem: using JPA (Java Persistence API) instead of direct JDBC calls. Turns out the MySQL ReplicationDriver (used to load balance reads to slaves and send writes to the master) relies on the readOnly state of the Connection in order to decide whether it’s a read or a write. With direct JDBC calls, I could get the Connection and toggle the readOnly state as needed.
Hibernate Embeddable Objects are a really neat way to organize your data model. Especially, if you have the same few columns in a number of different tables, that all pertain to the same thing. The example commonly used is Addresses. You may have a number of tables that each have fields pertaining to address information and you don’t want to have to do all the mappings for each entity again and again. If the column names are the same across each table, you can just add an @Embeddable annotation.