迁移数据库时合并用户的 Android Room 数据库
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【中文标题】迁移数据库时合并用户的 Android Room 数据库【英文标题】：Merge user's Android Room database when migrating database 【发布时间】：2020-03-22 16:46:06 【问题描述】：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数据库内容的更新版本。
目前，如果我在不更改架构的情况下将新内容添加到数据库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”，它是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.
;
【问题讨论】：
【参考方案1】：这可能吗？ 是的。不过有点复杂。
简而言之，您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（如果使用房间迁移会很复杂，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，那么您可以获取资产数据库并复制新的非用户数据（如果用户的数据与非-用户数据）。
即使这不是那么简单。但是，这是一个简单的示例/scanario，基于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，这会通过添加新列来更改 otherdata 表（而不是 users 表）。
然后它会检查 sContext 是否不为空。
使用有效的上下文而不是硬编码路径。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");
这会通过 copyDatabaseFromAssets 方法将数据库从资产复制到默认数据库位置（如下所示）。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（但根据更改的架构进行更改）数据库依赖 OnConflictStrategy.IGNORE只插入新行。 userdata 表保持不变，因此用户的数据被重新定义。
显然这不适合更改的行。这里是 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 将所有内容放在一起（注意为方便起见，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（在更改新架构的相关代码并增加版本之后）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();
【讨论】：
【参考方案2】：是的，有可能。
一个先决条件是您的预发布数据库和应用程序数据库版本必须相同。例如，您的第一个版本将两个数据库都作为版本 1。现在是包含新数据的第二个版本将预发布的应用数据库版本更新为 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();
Prepopulate your Room database Docs
This medium article很好地解释了这一点
【讨论】：
【参考方案3】：是的，这是可能的！ 增加您的 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();
【讨论】：
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