In Relation To

Hey, Vlad. My name is Christian Beikov, and I am 25. I’m living with my girlfriend in Vienna, the capital city of Austria. I started working with Java EE technologies in school and continued to do so at my first job where I am still employed part-time. Next to my job, I am doing my master studies in Software Engineering at TU Wien which I am hopefully finishing next year.

My main interests are in distributed systems, database technologies and everything Java/JVM-related. In school, I came into contact with Java EE for the first time when I was by developing a JSF-based web app with Hibernate on top of GlassFish with NetBeans. When I started my job at Curecomp GmbH, I mainly worked with Eclipse and WebSphere and about 2 years ago, I managed to fully migrate the company’s development stack to WildFly and IntelliJ IDEA. During these migrations and the countless university assignment projects in which I have used Hibernate, I’ve stumbled upon one or another bug.

The work I am doing in open-source projects happens mostly in my free time. I like to give back something to the community, even if it’s just bug reports. Since I use Hibernate in so many projects, I also see my contributions as an investment in improving the overall quality of the projects I do.

At my day job, I am sometimes facing problems that I simply can’t workaround or doing a proper fix seems equally hard to me, which is how I justify fixing the Hibernate bug in the core. The deep knowledge that I gain from analyzing bugs and discussing features also helps me in my day job when reasoning about the behavior of Hibernate in certain situations which is a big plus.

Blaze-Persistence is a library on top of the JPA APIs. The core module provides a fluent query builder API that allows you to express queries in a Java DSL which should feel mostly intuitive. In addition to the standard features that are defined in JPA 2.1, it also implements support for some common functionality that already every JPA provider supports like for example aliasing fetch joins or entity joins. On top of that, Blaze-Persistence also provides deep integration with the JPA provider to support features like (recursive) CTEs or set operations like UNION, etc. Beware that the deep integration is currently only available for Hibernate since it is the provider I am mostly familiar with, but support for others is planned.

One of the greatest features that Blaze-Persistence makes possible are Entity Views which are to JPA entities roughly what views are to tables in the RDBMS sense. An Entity View is an interface or abstract class that represents the structure of a projection for an entity. It’s basically the definition of a DTO, with the difference that you only need to specify getter methods along with the projection for that attribute as JPQL expression. When you then apply the Entity View on a base query, it will contribute the JPQL expressions as select items, thus creating an optimized JPQL and SQL query. The result of such a query, of course, is a list of objects that are a subtype of the Entity View. Apart from avoiding all the manual plumbing code to get the data into shape, you can make use of features like Collection mappings, Subviews or SubqueryProviders which let you define complex projections that one would normally not do.

The Criteria API provided by JPA is hard to use as it requires a lot of typing and also some kind of skill. You need to know how to wire things up which is one of the big pain points that I tried to solve by introducing a fluent API. Sure the JPA Criteria API is type-safe, but that comes at the cost of obfuscating your query. A type-safe variant of the Blaze-Persistence core API or maybe even just some additional methods in the existing API are already on my roadmap, so I will also try to fill this gap while retaining readability.

Since I don’t expect everyone to rewrite his existing JPA Criteria API based queries, I also implemented the JPA Criteria API on top of the Blaze-Persistence core API. You can even let your existing code build the queries with the JPA Criteria API and retrieve a Blaze-Persistence query builder from it. The resulting query builder can be used just like any other query builder which means you can use CTEs and all the other great features.

Just as a disclaimer, I haven’t dug too much into the communities of the other JPA providers as I don’t use them in any of my projects. Also, beware that I might be biased now since I know people from the Hibernate team and know who to contact if I have a problem, but I’ll try to be as neutral as possible.

I got the feeling that the EclipseLink community didn’t care about the bugs I reported or forum posts I did, but apart from that, the implementation seems ok. It has some quirks like e.g. allowing lazy loading although the underlying entity manager is closed, but maybe that’s a feature :D

DataNucleus which is one of the lesser known JPA providers is actually pretty good and the main developer there reacts super fast to bug reports. I found some bugs and also proposed some features to increase Hibernate compatibility and as far as I know, all of these issues have been resolved by now.

I can’t tell you much about OpenJPA except that it seems rather dead or in maintenance mode only to me. The latest version is only JPA 2.0 compatible and unfortunately, lacks even proprietary ways to do certain things that are possible with other JPA providers.

The thing I am mostly unsatisfied with is that most of the issues I found with any JPA provider are pretty basic things and should be asserted by the JPA TCK. I hope some Oracle guy who can actually do something reads this and pushes harder to make the JPA TCK open-source :)

I think Hibernate already does a very good job. What I really would like to see is the decoupling of the SQL generation and execution from the ORM specifics. This is something I often would have needed in one way or another to workaround bugs or simply to execute the SQL that is needed for a specific task. Imagine you could specify a HQL query that just describes how the result mapping should be done, but specify your own SQL. This is something I am doing internally in Blaze-Persistence all the time for advanced queries. I hope the SQM feature that is planned for Hibernate 6 will allow me to do that so I can get rid of the dirty tricks I have to do right now to get stuff done.