我正在创建一个需要数据库的应用程序.我使用sqlite数据库浏览器创建它,这意味着我创建的应用程序,将我创建的数据库导入手机.
我创建的应用程序要求用户将数据输入数据库.升级数据库时,我希望保留用户输入的数据.
我的数据库帮助程序代码如下:
public class DatabaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/test.test/databases/";
private static String DB_NAME = "TestDatabase";
private static final int DB_VERSION = 1;
private SQLiteDatabase myDatabase;
private final Context myContext;
/**
* # Constructor #
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
this.myContext = context;
}//constructor
/**
* # Create Database #
* Creates a empty database on the system and rewrites it with your own database.
*/
public void createDatabase() throws IOException {
boolean dbExist = checkDatabase();
if(dbExist)
{
//do nothing - database already exist
}//if
else
{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try
{
copyDatabase();
} catch (IOException e) {
throw new Error("Error copying database");
}//catch
}//else
}//createDatabase
private boolean checkDatabase() {
SQLiteDatabase checkDB = null;
try
{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch(SQLiteException e) {
//database does't exist yet.
}//catch
if(checkDB != null)
{
checkDB.close();
}//if
return checkDB != null ? true : false;
}//checkDatabase
private void copyDatabase() throws IOException {
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0)
{
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}//copyDatabase
// # open database #
public void openDatabase() throws SQLException {
//Open the database
String myPath = DB_PATH + DB_NAME;
myDatabase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}//openDatabase
@Override
public synchronized void close()
{
if(myDatabase != null)
myDatabase.close();
super.close();
}//close
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public List selectData
(String tableName, String [] columns, String selection, String[] selectionArgs,
String groupBy, String having, String orderBy) {
List list = new ArrayList();
Cursor cursor = this.myDatabase.query(tableName, columns, selection, selectionArgs, groupBy, having, orderBy);
if (cursor.moveToFirst())
{
do
{
list.add(cursor.getString(0));
}
while (cursor.moveToNext());
}
if (cursor != null && !cursor.isClosed())
{
cursor.close();
}
return list;
}//selectData
public void insertData (String tableName, String nullColumnHack, ContentValues values) {
try
{
myDatabase.insert(tableName, nullColumnHack, values);
} catch (Exception e) {
Log.e("Error :","unable to insert data");
}//catch
}//insertData
//edit row
public void updateData (String tableName, ContentValues values, String whereClause, String[] whereArgs) {
try
{
myDatabase.update(tableName, values, whereClause, whereArgs);
} catch (Exception e) {
Log.e("Error :","unable to update data");
}//catch
}//updateData
public void deleteRow (String tableName, String whereClause, String[] whereArgs) {
try
{
myDatabase.delete(tableName, whereClause, whereArgs);
} catch (Exception e) {
Log.e("Error :","unable to delete row");
}//catch
}//deleteRow
}
*注意:我的数据库由多个表组成.两个表需要用户输入.其他人没有.
我希望可以给出真正的答案,而不是给出我不具备的确切情况的网站,因为我很容易混淆.
您应该在onUpgrade方法中添加一些代码.这样,您可以检查oldVersion和newVersion并执行正确的ALTER TABLE语句.如您所见,当前版本为23,检查代码检查旧版本是什么.如果版本22它只执行v22语句,但是如果版本21它同时执行v21和v22语句.这是Google I/O应用的一部分:
private static final int VER_LAUNCH = 21;
private static final int VER_SESSION_FEEDBACK_URL = 22;
private static final int VER_SESSION_NOTES_URL_SLUG = 23;
private static final int DATABASE_VERSION = VER_SESSION_NOTES_URL_SLUG;
...
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.d(TAG, "onUpgrade() from " + oldVersion + " to " + newVersion);
// NOTE: This switch statement is designed to handle cascading database
// updates, starting at the current version and falling through to all
// future upgrade cases. Only use "break;" when you want to drop and
// recreate the entire database.
int version = oldVersion;
switch (version) {
case VER_LAUNCH:
// Version 22 added column for session feedback URL.
db.execSQL("ALTER TABLE " + Tables.SESSIONS + " ADD COLUMN "
+ SessionsColumns.SESSION_FEEDBACK_URL + " TEXT");
version = VER_SESSION_FEEDBACK_URL;
case VER_SESSION_FEEDBACK_URL:
// Version 23 added columns for session official notes URL and slug.
db.execSQL("ALTER TABLE " + Tables.SESSIONS + " ADD COLUMN "
+ SessionsColumns.SESSION_NOTES_URL + " TEXT");
db.execSQL("ALTER TABLE " + Tables.SESSIONS + " ADD COLUMN "
+ SessionsColumns.SESSION_SLUG + " TEXT");
version = VER_SESSION_NOTES_URL_SLUG;
}
Log.d(TAG, "after upgrade logic, at version " + version);
if (version != DATABASE_VERSION) {
Log.w(TAG, "Destroying old data during upgrade");
db.execSQL("DROP TABLE IF EXISTS " + Tables.BLOCKS);
// ... delete all your tables ...
onCreate(db);
}
}
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