inheritanceexample.java

db4o db4o是一个嵌入式的开源对象数据库引擎.对于Java与.NET开发者来说都是一个非常好的对象持久化工具. db4o性能高并且安装简单.

package com.db4o.f1.chapter4;

import java.io.*;
import java.util.Arrays;

import com.db4o.*;
import com.db4o.f1.*;
import com.db4o.query.*;


public class InheritanceExample extends Util {
    public static void main(String[] args) {
        new File(Util.YAPFILENAME).delete();
        ObjectContainer db=Db4o.openFile(Util.YAPFILENAME);
        try {
            storeFirstCar(db);
            storeSecondCar(db);
            retrieveTemperatureReadoutsQBE(db);
            retrieveAllSensorReadoutsQBE(db);
            retrieveAllSensorReadoutsQBEAlternative(db);
            retrieveAllSensorReadoutsQuery(db);
            retrieveAllObjectsQBE(db);
        }
        finally {
            db.close();
        }
    }

    public static void storeFirstCar(ObjectContainer db) {
        Car car1=new Car("Ferrari");
        Pilot pilot1=new Pilot("Michael Schumacher",100);
        car1.setPilot(pilot1);
        db.set(car1);
    }
    
    public static void storeSecondCar(ObjectContainer db) {
        Pilot pilot2=new Pilot("Rubens Barrichello",99);
        Car car2=new Car("BMW");
        car2.setPilot(pilot2);
        car2.snapshot();
        car2.snapshot();
        db.set(car2);
    }

    public static void retrieveAllSensorReadoutsQBE(
            ObjectContainer db) {
        SensorReadout proto=new SensorReadout(null,null,null);
        ObjectSet result=db.get(proto);
        listResult(result);
    }

    public static void retrieveTemperatureReadoutsQBE(
            ObjectContainer db) {
        SensorReadout proto=
            new TemperatureSensorReadout(null,null,null,0.0);
        ObjectSet result=db.get(proto);
        listResult(result);
    }

    public static void retrieveAllSensorReadoutsQBEAlternative(
            ObjectContainer db) {
        ObjectSet result=db.get(SensorReadout.class);
        listResult(result);
    }

    public static void retrieveAllSensorReadoutsQuery(
            ObjectContainer db) {
        Query query=db.query();
        query.constrain(SensorReadout.class);
        ObjectSet result=query.execute();
        listResult(result);
    }
    
    public static void retrieveAllObjectsQBE(ObjectContainer db) {
        ObjectSet result=db.get(new Object());
        listResult(result);
    }
    
}