java - 迁移数据库时合并用户的 Android Room 数据库

Question

我有一个 Room 数据库，其预加载的数据存储在 asset/database 中。我正在创建一个更新版本，其中包含数据库中的更多内容以供下次更新。

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“Collection 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.
    }
};

Answer 1

Is this possible? Yes. However it is a little complex.

简而言之，您实际上可以反过来做。而不是使用 Assets 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，因为迁移时您处于事务中)。

但是，如果您对正在使用的数据库而不是 Assets 数据库进行架构更改，则可以获取 Assets 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在一起，将会变得非常复杂)。

即使这也不是那么简单。然而，这里有一个简单的 exmaple/scanario，它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!!!!");
        }
    }
};

正如您所看到的，这通过添加新列更改了其他数据表(而不是用户表)。

然后检查 sContext 是否不为 null。

• 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");
}

• 注释掉了故意留下的代码，因为在尝试附加从 Assets 复制的数据库时遇到问题，因此恢复为使用单独的连接。

这将通过 copyDatabaseFromAssets 方法将数据库从 Assets 复制到默认数据库位置(如下所示)。它从 Assets 数据库中提取所有非用户数据，并将其插入原始(但根据更改后的架构进行更改)数据库依赖OnConflictStrategy.IGNORE仅插入新行。 userdata 表未受影响，因此用户的数据被保留。

• 显然这无法满足更改的行的需求。

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，它将所有这些组合在一起(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(更改新架构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(请注意，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();
    }
}