The reversetutorial.Finder class lets you run queries in JDOQL (JDO's Java-centric query syntax) against the existing database:

java reversetutorial.Finder <jdoql-query>
	

JDOQL looks exactly like Java boolean expressions. To find magazines matching a set of criteria in JDOQL, just specify conditions on the reversetutorial.Magazine class' persistent fields. Some examples of valid JDOQL queries for magazines include:

java reversetutorial.Finder "true"	// use this to list all the magazines
java reversetutorial.Finder "price < 5.0"
java reversetutorial.Finder "name == \"Vogue\" || issue > 1000"
java reversetutorial.Finder "name.startsWith (\"V\")"
	

To traverse object relations, just use Java's dot syntax:

java reversetutorial.Finder "publisher.name == \"Adventure\" || publisher.revenue > 1000000"
	

To traverse collection relations, you have to use JDOQL variables. Variables are just placeholders for any member of a collection. For example, in the following query, art is a variable:

java reversetutorial.Finder "articles.contians (art) && art.title.startsWith (\"JDO\")"
	

The above query is equivalent to "find all magazines who have an article whose title starts with 'JDO'". The reversetutorial.Finder pre-defines two variables you can use: Article art; Magazine mag;. With these, you can create very complex queries. For example, to find all magazines whose publisher published an article about "Surpassing Hubble" in any of its magazines:

java reversetutorial.Finder "publisher.magazines.contains (mag) && mag.articles.contains (art) && art.articleSubtitles.contains (\"Surpassing Hubble\")"
	

Have fun experimenting with additional queries.