db4o Storing/Retrieving/Updating/Deleting structured objects

Pilot { string name;   int point;   } 

Car  { string model;  Pilot pilot; }

// storeFirstCar
Car car1=new Car("Ferrari");
Pilot pilot1=new Pilot("Michael Schumacher",100);
car1.setPilot(pilot1);//保存Car时，默认也保存Pilot了
db.set(car1);

///////////////////////////////////////////////////////////////////////////////

// retrieveCarByPilotQBE
Pilot pilotproto=new Pilot("Rubens Barrichello",0);
Car carproto=new Car(null);
carproto.setPilot(pilotproto);
ObjectSet result=db.get(carproto);
listResult(result);

// retrieveCarsByPilotNameNative
final String pilotName = "Rubens Barrichello";
ObjectSet results = db.query(new Predicate() {
    public boolean match(Car car){
        return car.getPilot().getName().equals(pilotName);
    }
});
listResult(results);

// retrieveCarByPilotNameQuery
Query query=db.query();
query.constrain(Car.class);
query.descend("pilot").descend("name")
        .constrain("Rubens Barrichello");
ObjectSet result=query.execute();
listResult(result);

// retrieveCarByPilotProtoQuery
Query query=db.query();
query.constrain(Car.class);
Pilot proto=new Pilot("Rubens Barrichello",0);
query.descend("pilot").constrain(proto);
ObjectSet result=query.execute();
listResult(result);

//////////////////////////////////////////////////////////////////////////////////

更新Car时,需要注意的地方

// updatePilotSeparateSessionsImprovedPart1
Db4o.configure().objectClass("com.db4o.f1.chapter2.Car")
        .cascadeOnUpdate(true);//修改更新级联为真

// updatePilotSeparateSessionsImprovedPart2
ObjectSet result=db.query(new Predicate() {
    public boolean match(Car car){
        return car.getModel().equals("Ferrari");
    }
});
Car found=(Car)result.next();
found.getPilot().addPoints(1);
db.set(found);//更新Pilot的分数

// updatePilotSeparateSessionsImprovedPart3
ObjectSet result=db.query(new Predicate() {
    public boolean match(Car car){
        return car.getModel().equals("Ferrari");
    }
});
listResult(result);

///////////////////////////////////////////////////////////////////////////////

//删除要注意的地方

// deleteDeepPart1
Db4o.configure().objectClass("com.db4o.f1.chapter2.Car")
        .cascadeOnDelete(true);//设置删除级联为真

// deleteDeepPart2
ObjectSet result=db.query(new Predicate() {
    public boolean match(Car car){
        return car.getModel().equals("BMW");
    }
});
Car found=(Car)result.next();
db.delete(found);//删除Car以后,Pilot也被删除了
result=db.query(new Predicate() {
    public boolean match(Car car){
        return true;
    }
});
listResult(result);