我正在开发一个必须使用两个数据库的应用程序。我想将新数据库表中的记录添加到旧数据库表中，我已将新数据库放在我项目的 Assets 文件夹中，我可以使用新数据库和旧数据库进行查询。
问题是，当我尝试使用 onUpgrade() 方法将新数据库附加到旧数据库时，发生了一个错误，即无法在事务中附加数据库。
我发现很多链接都有这个问题，我已经尝试了很多但都没有成功。我是 SQLite 和 Android 的新手，请告诉我如何在代码中将数据库附加到另一个数据库。
数据库助手类:DatabaseHelper.java
public class DatabaseHelper extends SQLiteOpenHelper {
Context context;
SQLiteDatabase sourceDatabase;
private String TAG = this.getClass().getSimpleName();
private static final String DATABASE_NAME = "namesdemo_db";
private static final String SOURCE_DB_NAME = "namesdemo_db_s";
private static final int DATABASE_VERSION = 23;
private String DATABASE_PATH;
File dbFile;
// TABLE NAMES
private static final String TABLE_EMPLOYEE = "employee";
private static final String TABLE_FAVORITE = "fevorite";
// KEYS of Table Employee
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_ADDRESS = "address";
// Keys of Table Fevorite
private static final String KEY_FEV_ID = "fev_id";
// private static final String KEY_ID = "id";
private static final String CREATE_TBL_EMPLOYEE = "CREATE TABLE " + TABLE_EMPLOYEE + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_NAME
+ " TEXT," + KEY_ADDRESS + " TEXT)";
private static final String CREATE_TBL_FEVORITE = "CREATE TABLE " + TABLE_FAVORITE + "(" + KEY_FEV_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_ID
+ " INTEGER )";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
this.context = context;
DATABASE_PATH = "/data/data/" + context.getApplicationContext().getPackageName() + "/databases/";
Log.v(TAG, " DB Path " + DATABASE_PATH);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
Log.v(TAG, CREATE_TBL_EMPLOYEE);
db.execSQL(CREATE_TBL_EMPLOYEE);
db.execSQL(CREATE_TBL_FEVORITE);
Log.v(TAG, " OnCreate Executed");
}
private void copyDataBase(String dbPath) {
try {
InputStream assestDB = context.getAssets().open(SOURCE_DB_NAME);
OutputStream appDB = new FileOutputStream(dbPath + SOURCE_DB_NAME, false);
byte[] buffer = new byte[1024];
int length;
while ((length = assestDB.read(buffer)) > 0) {
appDB.write(buffer, 0, length);
}
appDB.flush();
appDB.close();
assestDB.close();
} catch (IOException e) {
e.printStackTrace();
}
Log.v(TAG, " copyDataBase() called");
}
public long createName(String name, String address) {
long count = 0;
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, name);
values.put(KEY_ADDRESS, address);
count = db.insert(TABLE_EMPLOYEE, null, values);
db.close();
Log.v(TAG, +count + " row(s) inserted!");
return count;
}
public long createFevorite(int id) {
long count = 0;
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_ID, id);
count = db.insert(TABLE_FAVORITE, null, values);
db.close();
Log.v(TAG, +count + " row(s) inserted in " + TABLE_FAVORITE);
return count;
}
public List<Employee> getAllNames() {
List<Employee> nameList = new ArrayList<Employee>();
String query = "Select * from " + TABLE_EMPLOYEE;
SQLiteDatabase db = getReadableDatabase();
Cursor c = db.rawQuery(query, null);
if (c.moveToFirst()) {
do {
Employee e = new Employee();
e.setID(c.getInt(c.getColumnIndex(KEY_ID)));
e.setName(c.getString(c.getColumnIndex(KEY_NAME)));
e.setAddress(c.getString(c.getColumnIndex(KEY_ADDRESS)));
nameList.add(e);
} while (c.moveToNext());
}
return nameList;
}
public List<Employee> getAllNames(SQLiteDatabase db) {
List<Employee> nameList = new ArrayList<Employee>();
String query = "Select * from " + TABLE_EMPLOYEE;
Cursor c = db.rawQuery(query, null);
if (c.moveToFirst()) {
do {
Employee e = new Employee();
e.setID(c.getInt(c.getColumnIndex(KEY_ID)));
e.setName(c.getString(c.getColumnIndex(KEY_NAME)));
e.setAddress(c.getString(c.getColumnIndex(KEY_ADDRESS)));
nameList.add(e);
Log.v(TAG, "ID: " + e.getID());
Log.v(TAG, "NAme: " + e.getName());
Log.v(TAG, "Address" + e.getAddress());
} while (c.moveToNext());
}
return nameList;
}
private boolean checkDatabase() {
// SQLiteDatabase checkdb = null;
boolean checkdb = false;
try {
String myPath = DATABASE_PATH + SOURCE_DB_NAME;
File dbfile = new File(myPath);
// checkdb =
// SQLiteDatabase.openDatabase(myPath,null,SQLiteDatabase.OPEN_READWRITE);
checkdb = dbfile.exists();
} catch (SQLiteException e) {
System.out.println("Database doesn't exist");
}
return checkdb;
}
public void openDatabase() throws SQLException {
String path = DATABASE_PATH + "namesdemo_db_s";
sourceDatabase = SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READWRITE);
Log.v(TAG, " openDatabase() called ");
}
public synchronized void closeDatabase() {
if (sourceDatabase != null) {
sourceDatabase.close();
Log.v(TAG, " closeDatabase() called ");
}
super.close();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
String drop_tbl = "DROP TABLE " + TABLE_EMPLOYEE;
String attach_db = "ATTACH DATABASE '" + SOURCE_DB_NAME + "' AS 'temp_db'";
String create_table = "CREATE TABLE " + TABLE_EMPLOYEE + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_NAME + " TEXT," + KEY_ADDRESS
+ " TEXT)";
String insert = "INSERT INTO " + TABLE_EMPLOYEE + "(" + KEY_ID + "," + KEY_NAME + "," + KEY_ADDRESS + ") SELECT * FROM temp_db." + TABLE_EMPLOYEE;
boolean dbExists = checkDatabase();
if (dbExists) {
Log.v(TAG, " DB exists");
// getAllNames(sourceDatabase);
} else {
Log.v(TAG, " DB does not exists");
copyDataBase(DATABASE_PATH);
// openDatabase();
// getAllNames(sourceDatabase);
}
db.execSQL(attach_db);
openDatabase();
//db.endTransaction();
db.execSQL(drop_tbl);
db.execSQL(create_table);
db.execSQL(insert);
Log.v(TAG, " onUpgrade() Executed");
db.close();
sourceDatabase.close();
}
最佳答案
我找到了 2 种附加数据库的方法。
不要在
onCreate和onUpgrade中“附加数据库”。它会因为“无法在事务中附加数据库”而失败。 但是您可以在初始化数据库时附加数据库，然后调用getReadableDatabase()以确保创建和升级数据库。 然后你可以运行附加命令。sqLiteHelper = new SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION); // new SQLiteOpenHelper SQLiteDatabase db = sqLiteHelper.getReadableDatabase(); // make sure the database will be created db.execSQL("ATTACH DATABASE '/databases/xx.db' AS xx;"); // do attach database但是如果您想在 onUpgrade() 之前附加，请尝试以下方式:
在 onCreate() 中结束事务，然后附加，然后开始事务
public void onCreate(SQLiteDatabase db) {
this.createTables(db); // do the normal onCreate() stuff
db.setTransactionSuccessful();
db.endTransaction(); // end transaction, so that you can do attach
db.execSQL("ATTACH DATABASE '/databases/xx.db' AS xx;"); // do attach database
db.execSQL("DETACH DATABASE xx;"); // detach database
db.beginTransaction(); // begin transation again
}
原因:
看了SQLiteOpenHelper.java的函数，发现onCreate()和onUpgrade()是在transaction的时候一起调用的。
关于android - 无法在事务中附加数据库，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28211644/