The EclipseStore engine takes care of persisting your object graph. When you do queries, they are not run on the data stored by EclipseStore, queries run on your data in the local system memory. There is no need to use special query languages like SQL. All operations can be done with plain Java. EclipseStore does not restrict you in the way you query your object graph. You are totally free to choose the best method fitting to your application.

One possibility may be Streams if you use the standard Java collections.

public List<Article> getUnAvailableArticles()
	return shop.getArticles().stream()
		.filter(a -> !a.available())
Of course you must care about lazy loading if you use that feature.