Debugging Hibernate Generated SQL

In this article, I will explain how to debug Hibernate’s generated SQL so that unexpected query results be traced faster either to a faulty dataset or a bug in the query.

There’s no need to present Hibernate anymore. Yet, for those who lived in a cave for the past years, let’s say that Hibernate is one of the two main ORM frameworks (the second one being TopLink) that dramatically ease database access in Java.

One of Hibernate’s main goal is to lessen the amount of SQL you write, to the point that in many cases, you won’t even write one line. However, chances are that one day, Hibernate’s fetching mechanism won’t get you the result you expected and the problems will begin in earnest. From that point and before further investigation, you should determine which is true:

   * either the initial dataset is wrong
   * or the generated query is
   * or both if you’re really unlucky

Being able to quickly diagnose the real cause will gain you much time. In order to do this, the greatest step will be viewing the generated SQL: if you can execute it in the right query tool, you could then compare pure SQL results to Hibernate’s results and assert the true cause. There are two solutions for viewing the SQL.
Show SQL

The first solution is the simplest one. It is part of Hibernate’s configuration and is heavily documented. Just add the following line to your hibernate.cfg.xml file:

<hibernate-configuration>
 <session-factory>
...
   <property name="hibernate.show_sql">true</property>
 </session-factory>
</hibernate-configuration>

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