我有一个 Room 数据库，它与预加载的数据一起存储在 assets/database 中。我正在为下一次更新创建一个包含更多内容的更新版本。
目前，如果我在没有架构更改的情况下向数据库添加新内容并重新安装应用程序，这些新内容不会显示。我可以看到更改的唯一方法是卸载并重新安装该应用程序。但是，我需要将用户的数据与具有新内容的数据库合并，因为我需要获取用户的“收藏夹”，这是一个包含项目内容的表的整数列。
这可能吗？
这就是我创建数据库的方式。
public static AppDatabase getInMemoryDatabase(Context context) {
if (INSTANCE == null) {
synchronized (AppDatabase.class) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, "app_database.db")
.createFromAsset("database/QuotesDB.db")
.addMigrations(MIGRATION_1_2)
.build();
}
}
}
return INSTANCE;
}
我尝试使用以下代码进行迁移，但它仍然没有更新内容。
/**
* Migrate from:
* version 1 - initial contents.
* to
* version 2 - updated database contents (no schema changes)
*/
@VisibleForTesting
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(SupportSQLiteDatabase database) {
// I need to tell Room that it should use the data
// from version 1 ( with the user's favorites ) to version 2.
}
};
这可能吗？ 是的。然而它有点复杂。
简而言之，你实际上可以反过来做。而不是使用资产中的新数据库并尝试检索以前的数据（如果使用 Room Migration 会很复杂，因为您必须有效地交换到新创建/复制的数据库，这会更加复杂，因为您在迁移时处于事务中） .
但是，如果您对正在使用的数据库而不是资产数据库进行架构更改，则可以获取资产数据库并复制新的非用户数据（如果用户数据与非用户数据混合，将会非常复杂数据）。
即使这样也不是那么简单。但是，这是一个简单的示例/scanario，它基于对您的代码的轻微扩展：-
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(SupportSQLiteDatabase db) {
final String TAG = "MIGRATE_1_2";
Log.d(TAG,"Database Version when called is " + db.getVersion());
// I need to tell Room that it should use the data
// from version 1 ( with the user's favorites ) to version 2.
// "CREATE TABLE IF NOT EXISTS `userdata` (`userId` INTEGER DEFAULT uid, `name` TEXT, PRIMARY KEY(`userId`))"
//db.execSQL("CREATE TABLE IF NOT EXISTS `userdata_saveuserdata` (`userId` INTEGER, `name` TEXT, PRIMARY KEY(`userId`))");
//db.execSQL("INSERT INTO `userdata_saveuserdata` SELECT * FROM `userdata`");
db.execSQL("ALTER TABLE `otherdata` ADD COLUMN `column2` TEXT");
Log.d(TAG,"Checking Context");
if (sContext != null) {
applyAssetDB(db);
} else {
Log.d(TAG,"Context is null!!!!");
}
}
};
如您所见，这通过添加新列更改了其他数据表（不是用户表）。
然后检查 sContext 是否不为空。
然后调用applyAssetDB，即：-
private static void applyAssetDB(SupportSQLiteDatabase sdb) {
String TAG = "APPLYASSETDB";
String mainDatabaseName = (new File(sdb.getPath()).getName());
String assetDatabaseName = mainDatabaseName + "_asset";
String asset_schema = "asset_schema";
Log.d(TAG,"Attempting application of asset data to database."
+ "\n\tActual Database = " + mainDatabaseName
+ "\n\tAsset Database will be " + assetDatabaseName
+ "\n\tSchema for attached database will be " + asset_schema
);
copyDatabaseFromAssets(AppDatabase.sContext,MainActivity.ASSETNAME,assetDatabaseName);
/*
if (sdb.isWriteAheadLoggingEnabled()) {
setAssetDBToWALMode(sContext.getDatabasePath(assetDatabaseName).getPath());
}
Log.d(TAG,"Attempting to ATTACH asset database " + sContext.getDatabasePath(assetDatabaseName).getPath() + "." + asset_schema);
sdb.execSQL("ATTACH DATABASE '" + sContext.getDatabasePath(assetDatabaseName).getPath() + "' AS " + asset_schema);
Log.d(TAG,"Attempting INSERTING NEW DATA using\n\t" + "INSERT OR IGNORE INTO `otherdata` SELECT * FROM `otherdata`." + asset_schema);
sdb.execSQL("INSERT OR IGNORE INTO `otherdata` SELECT * FROM `otherdata`." + asset_schema);
Log.d(TAG,"Attempting to DETACH " + sContext.getDatabasePath(assetDatabaseName).getPath() + "." + asset_schema);
sdb.execSQL("DETACH DATABASE '" + sContext.getDatabasePath(assetDatabaseName).getPath() + "." + asset_schema);
*/
int insertRows = 0;
SQLiteDatabase assetdb = SQLiteDatabase.openDatabase(sContext.getDatabasePath(assetDatabaseName).getPath(),null,SQLiteDatabase.OPEN_READONLY);
Cursor assetCursor = assetdb.query("`otherdata`",null,null,null,null,null,null);
ContentValues cv = new ContentValues();
while (assetCursor.moveToNext()) {
cv.clear();
for (String c: assetCursor.getColumnNames()) {
if (assetCursor.getType(assetCursor.getColumnIndex(c)) == Cursor.FIELD_TYPE_BLOB) {
cv.put(c,assetCursor.getBlob(assetCursor.getColumnIndex(c)));
} else {
cv.put(c,assetCursor.getString(assetCursor.getColumnIndex(c)));
}
}
if (sdb.insert("`otherdata`", OnConflictStrategy.IGNORE,cv) > 0 ) insertRows++;
}
Log.d(TAG,"Inserted " + insertRows + " from the Asset Database");
assetCursor.close();
Log.d(TAG,"Deleting " + sContext.getDatabasePath(assetDatabaseName).getPath());
if ((new File(sContext.getDatabasePath(assetDatabaseName).getPath())).delete()) {
Log.d(TAG,"Copied AssetDatabase successfully deleted.");
} else {
Log.d(TAG,"Copied Asset Database file not deleted????");
}
Log.d(TAG,"Finished");
}
这将通过 copyDatabaseFromAssets 方法（如下所示）将数据库从资产复制到默认数据库位置。它从资产数据库中提取所有非用户的数据并将其插入到原始（但根据更改的模式进行更改）数据库依赖 OnConflictStrategy.IGNORE 仅插入新行。 userdata 表未被修改，因此用户的数据被重新定义。
这是 copyDatabaseFromAssets
private static void copyDatabaseFromAssets(Context context, String assetName, String databaseName) {
String TAG = "COPYDBFROMASSET";
int bufferSize = 1024 * 4, length = 0, read = 0, written = 0, chunks = 0;
byte[] buffer = new byte[bufferSize];
try {
Log.d(TAG,"Attempting opening asset " + assetName + " as an InputFileStream.");
InputStream is = context.getAssets().open(assetName);
Log.d(TAG,"Attempting opening FileOutputStream " + context.getDatabasePath(databaseName).getPath());
OutputStream os = new FileOutputStream(context.getDatabasePath(databaseName));
Log.d(TAG,"Initiating copy.");
while((length = is.read(buffer)) > 0) {
read += length;
os.write(buffer,0,length);
written += length;
chunks++;
}
Log.d(TAG,"Read " + read + "bytes; Wrote " + written + " bytes; in " + chunks);
Log.d(TAG,"Finalising (Flush and Close output and close input)");
os.flush();
os.close();
is.close();
Log.d(TAG,"Finalised");
} catch (IOException e) {
throw new RuntimeException("Error copying Database from Asset " + e.getMessage());
}
}
这是一个示例 Activity MainActivity 将它们放在一起（请注意，为了方便起见，我使用了 allowMainThreadQueries ）：-
public class MainActivity extends AppCompatActivity {
//public static final int DBVERSION = 1; //!!!!! ORIGINAL
public static final int DBVERSION = 2;
public static final String DBNAME = "app_database.db";
public static final String ASSETNAME = "database/QuotesDB.db";
AppDatabase appDB;
AllDao adao;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
appDB.setContext(this);
appDB = Room.databaseBuilder(this,AppDatabase.class,DBNAME)
.allowMainThreadQueries()
.createFromAsset(ASSETNAME)
.addCallback(AppDatabase.CALLBACK)
.addMigrations(AppDatabase.MIGRATION_1_2)
.build();
adao = appDB.allDao();
appDB.logDBInfo();
if (adao.getUserDataRowCount() == 3) {
adao.insertOneUserData(new UserData("ADDEDU100"));
adao.insertOneUserData(new UserData("ADDEDU200"));
adao.insertOneUserData(new UserData("ADDEDU300"));
}
appDB.logDBInfo();
}
}
运行时（更改新模式的相关代码并增加版本后）日志中的结果是：-
2019-11-30 10:56:38.768 12944-12944/a.roommigrationwithassets D/MIGRATE_1_2: Database Version when called is 1
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/MIGRATE_1_2: Checking Context
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/APPLYASSETDB: Attempting application of asset data to database.
Actual Database = app_database.db
Asset Database will be app_database.db_asset
Schema for attached database will be asset_schema
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/COPYDBFROMASSET: Attempting opening asset database/QuotesDB.db as an InputFileStream.
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/COPYDBFROMASSET: Attempting opening FileOutputStream /data/user/0/a.roommigrationwithassets/databases/app_database.db_asset
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/COPYDBFROMASSET: Initiating copy.
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/COPYDBFROMASSET: Read 12288bytes; Wrote 12288 bytes; in 3
2019-11-30 10:56:38.771 12944-12944/a.roommigrationwithassets D/COPYDBFROMASSET: Finalising (Flush and Close output and close input)
2019-11-30 10:56:38.772 12944-12944/a.roommigrationwithassets D/COPYDBFROMASSET: Finalised
2019-11-30 10:56:38.780 12944-12944/a.roommigrationwithassets D/APPLYASSETDB: Inserted 3 from the Asset Database
2019-11-30 10:56:38.780 12944-12944/a.roommigrationwithassets D/APPLYASSETDB: Deleting /data/user/0/a.roommigrationwithassets/databases/app_database.db_asset
2019-11-30 10:56:38.780 12944-12944/a.roommigrationwithassets D/APPLYASSETDB: Copied AssetDatabase successfully deleted.
2019-11-30 10:56:38.780 12944-12944/a.roommigrationwithassets D/APPLYASSETDB: Finished
2019-11-30 10:56:38.815 12944-12944/a.roommigrationwithassets D/ONOPEN: Database Version when called is 2
2019-11-30 10:56:38.816 12944-12944/a.roommigrationwithassets D/ONOPEN: Database Version after Super call is 2
2019-11-30 10:56:38.819 12944-12944/a.roommigrationwithassets D/DBINFO: UserData rowcount = 6
ID = 1 NAME = OU1
ID = 2 NAME = OU2
ID = 3 NAME = OU3
ID = 4 NAME = ADDEDU100
ID = 5 NAME = ADDEDU200
ID = 6 NAME = ADDEDU300
OtherData rowcount = 3
ID = 1Column1 = OD1
ID = 2Column1 = OD2
ID = 3Column1 = OD3
2019-11-30 10:56:38.821 12944-12944/a.roommigrationwithassets D/DBINFO: UserData rowcount = 6
ID = 1 NAME = OU1
ID = 2 NAME = OU2
ID = 3 NAME = OU3
ID = 4 NAME = ADDEDU100
ID = 5 NAME = ADDEDU200
ID = 6 NAME = ADDEDU300
OtherData rowcount = 3
ID = 1Column1 = OD1
ID = 2Column1 = OD2
ID = 3Column1 = OD3
AppDatabase 类的完整代码（注意这包括一些冗余代码）是：-
@Database(version = MainActivity.DBVERSION, exportSchema = false,entities = {UserData.class,OtherData.class})
abstract class AppDatabase extends RoomDatabase {
abstract AllDao allDao();
static Context sContext;
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(SupportSQLiteDatabase db) {
final String TAG = "MIGRATE_1_2";
Log.d(TAG,"Database Version when called is " + db.getVersion());
// I need to tell Room that it should use the data
// from version 1 ( with the user's favorites ) to version 2.
// "CREATE TABLE IF NOT EXISTS `userdata` (`userId` INTEGER DEFAULT uid, `name` TEXT, PRIMARY KEY(`userId`))"
//db.execSQL("CREATE TABLE IF NOT EXISTS `userdata_saveuserdata` (`userId` INTEGER, `name` TEXT, PRIMARY KEY(`userId`))");
//db.execSQL("INSERT INTO `userdata_saveuserdata` SELECT * FROM `userdata`");
db.execSQL("ALTER TABLE `otherdata` ADD COLUMN `column2` TEXT");
Log.d(TAG,"Checking Context");
if (sContext != null) {
applyAssetDB(db);
} else {
Log.d(TAG,"Context is null!!!!");
}
}
};
static final RoomDatabase.Callback CALLBACK = new RoomDatabase.Callback() {
@Override
public void onCreate(@NonNull SupportSQLiteDatabase db) {
Log.d("ONCREATE","Database Version when called is " + db.getVersion());
super.onCreate(db);
Log.d("ONCREATE","Database Version after Super call is " + db.getVersion());
}
@Override
public void onOpen(@NonNull SupportSQLiteDatabase db) {
Log.d("ONOPEN","Database Version when called is " + db.getVersion());
super.onOpen(db);
Log.d("ONOPEN","Database Version after Super call is " + db.getVersion());
}
@Override
public void onDestructiveMigration(@NonNull SupportSQLiteDatabase db) {
Log.d("ONDESTRMIG","Database Version when called is " + db.getVersion());
super.onDestructiveMigration(db);
Log.d("ONDESTRMIG","Database Version after Super call is " + db.getVersion());
}
};
public void logDBInfo() {
AllDao adao = this.allDao();
List<UserData> allUserDataRows = adao.getAllUserDataRows();
StringBuilder sb = new StringBuilder().append("UserData rowcount = ").append(allUserDataRows.size());
for (UserData u: allUserDataRows) {
sb.append("\n\tID = ").append(u.getId()).append(" NAME = " + u.getName());
}
List<OtherData> allOtherDataRows = adao.getAllOtherDataRows();
sb.append("\n\nOtherData rowcount = ").append(allOtherDataRows.size());
for (OtherData o: allOtherDataRows) {
sb.append("\n\tID = ").append(o.getOtherDataId()).append("Column1 = ").append(o.getColumn1());
}
Log.d("DBINFO",sb.toString());
}
static void setContext(Context context) {
sContext = context;
}
private static void applyAssetDB(SupportSQLiteDatabase sdb) {
String TAG = "APPLYASSETDB";
String mainDatabaseName = (new File(sdb.getPath()).getName());
String assetDatabaseName = mainDatabaseName + "_asset";
String asset_schema = "asset_schema";
Log.d(TAG,"Attempting application of asset data to database."
+ "\n\tActual Database = " + mainDatabaseName
+ "\n\tAsset Database will be " + assetDatabaseName
+ "\n\tSchema for attached database will be " + asset_schema
);
copyDatabaseFromAssets(AppDatabase.sContext,MainActivity.ASSETNAME,assetDatabaseName);
/*
if (sdb.isWriteAheadLoggingEnabled()) {
setAssetDBToWALMode(sContext.getDatabasePath(assetDatabaseName).getPath());
}
Log.d(TAG,"Attempting to ATTACH asset database " + sContext.getDatabasePath(assetDatabaseName).getPath() + "." + asset_schema);
sdb.execSQL("ATTACH DATABASE '" + sContext.getDatabasePath(assetDatabaseName).getPath() + "' AS " + asset_schema);
Log.d(TAG,"Attempting INSERTING NEW DATA using\n\t" + "INSERT OR IGNORE INTO `otherdata` SELECT * FROM `otherdata`." + asset_schema);
sdb.execSQL("INSERT OR IGNORE INTO `otherdata` SELECT * FROM `otherdata`." + asset_schema);
Log.d(TAG,"Attempting to DETACH " + sContext.getDatabasePath(assetDatabaseName).getPath() + "." + asset_schema);
sdb.execSQL("DETACH DATABASE '" + sContext.getDatabasePath(assetDatabaseName).getPath() + "." + asset_schema);
*/
int insertRows = 0;
SQLiteDatabase assetdb = SQLiteDatabase.openDatabase(sContext.getDatabasePath(assetDatabaseName).getPath(),null,SQLiteDatabase.OPEN_READONLY);
Cursor assetCursor = assetdb.query("`otherdata`",null,null,null,null,null,null);
ContentValues cv = new ContentValues();
while (assetCursor.moveToNext()) {
cv.clear();
for (String c: assetCursor.getColumnNames()) {
if (assetCursor.getType(assetCursor.getColumnIndex(c)) == Cursor.FIELD_TYPE_BLOB) {
cv.put(c,assetCursor.getBlob(assetCursor.getColumnIndex(c)));
} else {
cv.put(c,assetCursor.getString(assetCursor.getColumnIndex(c)));
}
}
if (sdb.insert("`otherdata`", OnConflictStrategy.IGNORE,cv) > 0 ) insertRows++;
}
Log.d(TAG,"Inserted " + insertRows + " from the Asset Database");
assetCursor.close();
Log.d(TAG,"Deleting " + sContext.getDatabasePath(assetDatabaseName).getPath());
if ((new File(sContext.getDatabasePath(assetDatabaseName).getPath())).delete()) {
Log.d(TAG,"Copied AssetDatabase successfully deleted.");
} else {
Log.d(TAG,"Copied Asset Database file not deleted????");
}
Log.d(TAG,"Finished");
}
private static void copyDatabaseFromAssets(Context context, String assetName, String databaseName) {
String TAG = "COPYDBFROMASSET";
int bufferSize = 1024 * 4, length = 0, read = 0, written = 0, chunks = 0;
byte[] buffer = new byte[bufferSize];
try {
Log.d(TAG,"Attempting opening asset " + assetName + " as an InputFileStream.");
InputStream is = context.getAssets().open(assetName);
Log.d(TAG,"Attempting opening FileOutputStream " + context.getDatabasePath(databaseName).getPath());
OutputStream os = new FileOutputStream(context.getDatabasePath(databaseName));
Log.d(TAG,"Initiating copy.");
while((length = is.read(buffer)) > 0) {
read += length;
os.write(buffer,0,length);
written += length;
chunks++;
}
Log.d(TAG,"Read " + read + "bytes; Wrote " + written + " bytes; in " + chunks);
Log.d(TAG,"Finalising (Flush and Close output and close input)");
os.flush();
os.close();
is.close();
Log.d(TAG,"Finalised");
} catch (IOException e) {
throw new RuntimeException("Error copying Database from Asset " + e.getMessage());
}
}
private static void setAssetDBToWALMode(String assetDBPath) {
SQLiteDatabase db = SQLiteDatabase.openDatabase(assetDBPath,null,SQLiteDatabase.OPEN_READWRITE);
db.enableWriteAheadLogging();
db.close();
}
}
是的，这是可能的。
一个先决条件是你的预装数据库和应用程序数据库版本必须相同。 例如，你的第一个版本将两个数据库都作为版本 1。现在第二个版本的新数据更新预装和应用程序数据库版本为 2，您的数据库构建器代码将如下所示：
Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, "app_database.db")
.createFromAsset("database/QuotesDB.db")
.fallbackToDestructiveMigration()
.build();
这篇中篇文章很好地解释了这一点
是的，这是可能的！ 增加 SQLite VERSION 并在 Room.databaseBuilder() 中添加 .fallbackToDestructiveMigration()
Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, "app_database.db")
.createFromAsset("database/QuotesDB.db")
.fallbackToDestructiveMigration()
.build();
在这里结束了类似的问题，所以对于未来的读者：
我最终得到以下结果：
@Database(...) abstract class MainDatabase : RoomDatabase() {
// Default Singleton pattern code
companion object {
@Volatile private var INSTANCE: Database? = null
fun getDatabase(context: Context): Database {
return INSTANCE ?: synchronized(this) {
// Located here to have access to `Context`
val MIGRATION_17_18 = object : Migration(17, 18) {
override fun migrate(database: SupportSQLiteDatabase) {
// Check if `secondDb` exists
val file = context.getDatabasePath(SecondDatabase.DATABASE_NAME)
if (file.exists()) {
// Using a build method which includes all migation steps for `secondDb`
val secondDb = SecondDatabase.build(context)
// TODO: add handling for different `secondDb` versions
// Insert the data from the `secondDb`
secondDb.locationDao().all.forEach {
database.execSQL(
"INSERT INTO `Location` (`id`, ...)"
+ " VALUES ('" + it.uid + "', ...)"
)
}
// Drop `secondDb` (this also deleted temp files like `wal`, `sha`, etc.
context.deleteDatabase(SecondDatabase.DATABASE_NAME)
}
}
}
// Default building code for Singleton Pattern
val instance = Room.databaseBuilder(
context.applicationContext,
Database::class.java,
"mainDb"
)
.enableMultiInstanceInvalidation()
.addMigrations(MIGRATION_17_18)
.build()
INSTANCE = instance
return instance
}
}
}
}
我按照建议使用单例模式这里