我正在尝试使用 OrmLite 保存我的数据。在示例中有这个类：
package com.example.helloandroid;
import java.sql.SQLException;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import com.j256.ormlite.android.apptools.OrmLiteSqliteOpenHelper;
import com.j256.ormlite.dao.Dao;
import com.j256.ormlite.dao.RuntimeExceptionDao;
import com.j256.ormlite.support.ConnectionSource;
import com.j256.ormlite.table.TableUtils;
/**
* Database helper class used to manage the creation and upgrading of your database. This class also usually provides
* the DAOs used by the other classes.
*/
public class DatabaseHelper extends OrmLiteSqliteOpenHelper {
// name of the database file for your application -- change to something appropriate for your app
private static final String DATABASE_NAME = "helloAndroid.db";
// any time you make changes to your database objects, you may have to increase the database version
private static final int DATABASE_VERSION = 1;
// the DAO object we use to access the SimpleData table
private Dao<SimpleData, Integer> simpleDao = null;
private RuntimeExceptionDao<SimpleData, Integer> simpleRuntimeDao = null;
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION, R.raw.ormlite_config);
}
/**
* This is called when the database is first created. Usually you should call createTable statements here to create
* the tables that will store your data.
*/
@Override
public void onCreate(SQLiteDatabase db, ConnectionSource connectionSource) {
try {
Log.i(DatabaseHelper.class.getName(), "onCreate");
TableUtils.createTable(connectionSource, SimpleData.class);
} catch (SQLException e) {
Log.e(DatabaseHelper.class.getName(), "Can't create database", e);
throw new RuntimeException(e);
}
// here we try inserting data in the on-create as a test
RuntimeExceptionDao<SimpleData, Integer> dao = getSimpleDataDao();
long millis = System.currentTimeMillis();
// create some entries in the onCreate
SimpleData simple = new SimpleData(millis);
dao.create(simple);
simple = new SimpleData(millis + 1);
dao.create(simple);
Log.i(DatabaseHelper.class.getName(), "created new entries in onCreate: " + millis);
}
/**
* This is called when your application is upgraded and it has a higher version number. This allows you to adjust
* the various data to match the new version number.
*/
@Override
public void onUpgrade(SQLiteDatabase db, ConnectionSource connectionSource, int oldVersion, int newVersion) {
try {
Log.i(DatabaseHelper.class.getName(), "onUpgrade");
TableUtils.dropTable(connectionSource, SimpleData.class, true);
// after we drop the old databases, we create the new ones
onCreate(db, connectionSource);
} catch (SQLException e) {
Log.e(DatabaseHelper.class.getName(), "Can't drop databases", e);
throw new RuntimeException(e);
}
}
/**
* Returns the Database Access Object (DAO) for our SimpleData class. It will create it or just give the cached
* value.
*/
public Dao<SimpleData, Integer> getDao() throws SQLException {
if (simpleDao == null) {
simpleDao = getDao(SimpleData.class);
}
return simpleDao;
}
/**
* Returns the RuntimeExceptionDao (Database Access Object) version of a Dao for our SimpleData class. It will
* create it or just give the cached value. RuntimeExceptionDao only through RuntimeExceptions.
*/
public RuntimeExceptionDao<SimpleData, Integer> getSimpleDataDao() {
if (simpleRuntimeDao == null) {
simpleRuntimeDao = getRuntimeExceptionDao(SimpleData.class);
}
return simpleRuntimeDao;
}
/**
* Close the database connections and clear any cached DAOs.
*/
@Override
public void close() {
super.close();
simpleRuntimeDao = null;
}
}
它引用了 SimpleData 类。如果我想持久化各种类的对象，是否必须为我想持久化的每个类创建一个 DatabaseHelper 类？