The data knowledge stack

Concurrency is not for the faint-hearted We all know concurrency programming is difficult to get it right. That’s why threading tasks are followed by extensive design and code review sessions. You never assign concurrent issues to inexperienced developers. The problem space is carefully analyzed, a design emerges and the solution is both documented and reviewed. That’s how threading related tasks are usually addressed. You will naturally choose a higher level abstraction since you don’t want to get tangled up in low-level details. That’s why the java.util.concurrent is usually better (unless you build… Read More

How to detect the Hibernate N+1 query problem during testing

Introduction Hibernate simplifies CRUD operations, especially when dealing with entity graphs. But any abstraction has its price and Hibernate is no different. I’ve already talked about the importance of fetching strategy and knowing your Criteria SQL queries, but there is more you can do to rule over JPA. This post is about controlling the SQL statement count that Hibernate calls on your behalf. Before ORM tools got so popular, all database interactions were done through explicit SQL statements, and optimizations were mostly targeted towards slow queries. If you think that using Hibernate… Read More

Why you should always check the SQL statements generated by Criteria API

Introduction Criteria API is very useful for dynamically building queries, but that’s the only use case where I’d use it. Whenever you have a UI with N filters that may arrive in any M combinations, it makes sense to have an API to construct queries dynamically, since concatenating strings is always a path I’m running away from. The question is, are you aware of the SQL queries your Criteria API generates behind the scenes? I’ve been reviewing many such queries lately, and I’ve been struck by how easy it is to get… Read More

Hibernate integration testing strategies

Introduction I like integration testing. As I explained in this article, it’s a good way to check what SQL queries are generated by Hibernate behind the scenes. But integration tests require a running database server, and this is the first choice you have to make. Using a production-like local database server for Integration Testing For a production environment, I always prefer using incremental DDL scripts, since I can always know what version is deployed on a given server, and which scripts required to be deployed. I’ve been relying on Flyway to manage… Read More

How to fetch entities multiple levels deep with Hibernate

Introduction It’s quite common to retrieve a root entity along with its children associations on multiple levels. In our example, we need to load a Forest with its Trees and Branches and Leaves, and we will try to see have Hibernate behaves for three collection types: Sets, Indexed Lists, and Bags.