Hibernate: A Developer's Notebook

8.1. Using Simple Criteria

Let's start by building a criteria query to find tracks shorter than a specified length, replacing the HQL we used in Example 3-9 and updating the code of Example 8-10.

8.1.1. How do I do that?

The first thing we need to figure out is how to specify the kind of object we're interested in retrieving. There is no query language involved in building criteria queries. Instead, you build up a tree of Criteria objects describing what you want. The Hibernate Session acts as a factory for these criteria, and you start, conveniently enough, by specifying the type of objects you want to retrieve.

Edit QueryTest.java, replacing the contents of the tracksNoLongerThan() method with those shown in Example 8-1.

These examples assume the database has been set up as described in the preceding chapters. If you don't want to go through all that, download the sample code, then jump into this chapter and run the "codegen", "schema", and "ctest" targets.

Example 8-1. The beginnings of a criteria query

public static List tracksNoLongerThan(Time length, Session session) throws HibernateException { Criteria criteria = session.createCriteria(Track.class); return criteria.list(); }

The session's createCriteria() method builds a criteria query that will return instances of the persistent class you supply as an argument. Easy enough. If you run the example at this point, of course, you'll see all the tracks in the database, since we haven't gotten around to expressing any actual criteria ...