Query By Example

When using Query By Example(QBE) you provide db4o with a template object. db4o will return all of the objects which match all non-default field values. This is done via reflecting all of the fields and building a query expression where all non-default-value fields are combined with AND expressions. Here's a simple example:

PersistentExample.java: retrievePilotByName
1private static void retrievePilotByName(ObjectContainer container) { 2 Pilot proto = new Pilot("Michael Schumacher", 0); 3 ObjectSet result = container.get(proto); 4 listResult(result); 5 }

Querying this way has some obvious limitations:

For more information see QBE Limitations. To get around all of these constraints, db4o provides the Native Query (NQ) system.