我的应用版本1.0中包含带有离线数据存储的SQLite数据库。目的是用户可以搜索某些主题而无需互联网保持离线状态。现在在下一次更新中，我想将我的应用程序同步到Web服务，这样如果在Web服务上更新了新主题，那么我的应用程序会自动下载它们并存储在本地SQLite数据库中。对于这个新场景，我需要修改旧表以及想要创建一些新表。但是对于旧桌子我只想添加一些字段而不想丢失旧数据。所以现在我想，在我的下一次更新中，应用程序将删除以前的SQLite数据库并替换为这个新数据库。我读过this question但是被评论搞糊涂了，他们正在讨论删除旧表和创建新表。但在这种情况下，如何手动在新表中插入太多旧数据。
以下是我正在使用的DBHelper类：
public class DBHelper extends SQLiteOpenHelper {
public static String DB_PATH = "/data/data/com.example.myapp/databases/";
public static String DB_NAME = "myapp.db";
public static final int DB_VERSION = 1;
public static final String TB_TOPICS = "My_Topics";
private SQLiteDatabase myDB;
private Context context;
public DBHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
this.context = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
@Override
public synchronized void close(){
if(myDB!=null){
myDB.close();
}
super.close();
}
/***
* Open database
* @throws SQLException
*/
public void openDataBase() throws SQLException{
String myPath = DB_PATH + DB_NAME;
myDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
/***
* Copy database from source code assets to device
* @throws IOException
*/
public void copyDataBase() throws IOException{
try {
InputStream myInput = context.getAssets().open(DB_NAME);
String outputFileName = DB_PATH + DB_NAME;
OutputStream myOutput = new FileOutputStream(outputFileName);
byte[] buffer = new byte[1024];
int length;
while((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
} catch (Exception e) {
Log.e("tle99 - copyDatabase", e.getMessage());
}
}
/***
* Check if the database doesn't exist on device, create new one
* @throws IOException
*/
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
} else {
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
Log.e("tle99 - create", e.getMessage());
}
}
}
// ---------------------------------------------
// PRIVATE METHODS
// ---------------------------------------------
/***
* Check if the database is exist on device or not
* @return
*/
private boolean checkDataBase() {
SQLiteDatabase tempDB = null;
try {
String myPath = DB_PATH + DB_NAME;
tempDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
} catch (SQLiteException e) {
Log.e("tle99 - check", e.getMessage());
}
if (tempDB != null)
tempDB.close();
return tempDB != null ? true : false;
}
以下是我的方法我从活动方法调用数据库：
List<AVData> listAVData = new ArrayList<AVData>();
DBHelper dbHelper = new DBHelper(this);
try {
dbHelper.createDataBase();
} catch (IOException e) {
e.printStackTrace();
}
listAVData = dbHelper.getHeadings(topicToSearch.trim());
答案 0 :(得分：2)
尝试。
在SQLITEOpenHelper类
中public class YourHelperClassName extends SQLiteOpenHelper {
public YourHelperClassName(Context c) {
super(c, "YOUR_DBNAME", null, new_version_number);
}
@Override
public void onCreate(SQLiteDatabase db) {
//Add the Table creation code for new version here. Since this code works for the new user or when the user cleare data from settings.
}
然后OverRide onUpgrade方法并执行
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (oldVersion == your_old-version_number && newVersion == new_version_number) {
//1.Fetch Data from old table and Assign it in a Cursor.
//2.Drop the table and Create New Table or Alter the Table.
//3.Add data to the new table from the Cursor.
// If you are Altering the table it is not required to add the data again to the table
}
希望这可以帮助您解决问题。使用现有数据库进行升级比创建新数据库更好。您可以使用逻辑进行升级。在升级数据库代码时，不要将onCreate代码更改为新代码。