问通过从assert复制数据库文件在Room中使用预先填充的数据库
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Stack Overflow用户

提问于 2018-08-16 09:31:44

回答 4查看 3.8K关注 0票数 3

我想使用安卓机房的预置数据库。我找到了一种方法，通过使用回调，并填充数据库文件。但是有些地方不对劲，我确信数据库是正常复制的，但是在设备监视器和android仿真器中它仍然是空的。你能帮帮我吗

public abstract class AppDatabase extends RoomDatabase {
private static AppDatabase INSTANCE;
private static final String DB_NAME = "base.db";
static Context ctx;

public abstract Dao dao();

public static AppDatabase getDatabase(Context context) {
    if (INSTANCE == null) {
        ctx = context;
        synchronized (AppDatabase.class) {
            if (INSTANCE == null) {
                INSTANCE = Room.databaseBuilder(context,
                        AppDatabase.class, DB_NAME)
                        .allowMainThreadQueries()
                        .addCallback(rdc)
                        .build();
            }
        }
    }
    return INSTANCE;
}

private static RoomDatabase.Callback rdc = new RoomDatabase.Callback() {
    public void onCreate(SupportSQLiteDatabase db) {

        new PopulateDbAsync(INSTANCE, ctx).execute();
        Log.d("db create ", "table created when db created first time in  onCreate");
    }

    public void onOpen(@NonNull SupportSQLiteDatabase db) {
        ContentValues contentValues = new ContentValues();
    }
};

private static class PopulateDbAsync extends AsyncTask<Void, Void, Void> {

    private Dao dao;
    AssetManager assetManager = ctx.getAssets();

    PopulateDbAsync(AppDatabase db, Context context) {
        Dao = db.Dao();
        ctx = context;
    }

    @Override
    protected Void doInBackground(final Void... params) {
        String DB_PATH = "/data/data/mypackage/databases/";
        String DB_NAME = "base.db";
        try {
            Log.d("AppDatabase","Trying copy database file");
            OutputStream myOutput = new FileOutputStream(DB_PATH + DB_NAME);
            byte[] buffer = new byte[1024];
            int length;
            InputStream myInput = ctx.getAssets().open("base.db");
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }
            myInput.close();
            myOutput.flush();
            myOutput.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}
}

android-sqlite

filestream

android-room

populate

回答 4

Stack Overflow用户

回答已采纳

发布于 2019-01-06 06:40:53

我花了6个小时在研究和研发上解决了问题。

上下文是：-我想把已经存在的finaldb.db(它在assests文件夹中)放到房间数据库中。

步骤1 :从这里复制这个框架文件链接

步骤2:需要迁移的，我有代码:)

@Database(entities = {Status.class}, version = 1,exportSchema = false)
public abstract class AppDatabase extends RoomDatabase {
    public abstract DataDao StatusDao();

    private static AppDatabase INSTANCE;


    public static AppDatabase getDatabase(Context context) {
        if (INSTANCE == null) {
            INSTANCE = createDatabase(context);
        }
        return (INSTANCE);
    }

    private static final Migration MIGRATION_2_3 = new Migration(1, 2) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            Log.d("kkkk","bc");

            String SQL_CREATE_TABLE = "CREATE TABLE IF NOT EXISTS 'Status' " +
                    "( 'id' INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT," +
                    "  'category' TEXT NOT NULL," +
                    "  'sub_category' TEXT NOT NULL," +
                    "  'content' TEXT NOT NULL," +
                    "  'favourite' INTEGER DEFAULT(0))";

            database.execSQL(SQL_CREATE_TABLE);

        }
    };

    private static AppDatabase createDatabase(Context context) {
        RoomDatabase.Builder<AppDatabase> builder =
                Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class,
                        context.getString(R.string.dbase_name));


        return (builder.openHelperFactory(new AssetSQLiteOpenHelperFactory())
                .allowMainThreadQueries()
                .addMigrations(MIGRATION_2_3)
                .build());
    }

}

在MIGRATION_2_3中，您必须创建与当前数据库完全相同的表(该数据库存在于资产文件夹中)

想了解迁移

步骤3:在房间数据库中成功地创建了 Now表！

如果发生崩溃，请参阅您的logcat，其中以可理解的形式写成.。

票数 5

Stack Overflow用户

发布于 2018-08-16 12:30:03

您不能正确地在onCreate方法中复制数据库。

当调用onCreate方法时，已经创建了数据库(将创建的数据库传递给该方法)。您必须在onCreate方法之前和数据库打开之前进行复制。

您可以重写init方法的RoomDatabase，并从该方法执行副本，或者在调用databaseBuilder之前执行复制。

票数 2

Stack Overflow用户

发布于 2018-09-04 01:20:49

我解决了。数据库类：

@Database(entities = {Entity1.class, Entity2.class, Entity3.class}, version = 1, exportSchema = false)
public abstract class AppDatabase extends RoomDatabase {
private static AppDatabase INSTANCE;

public abstract Entity1Dao 1Dao();
public abstract Entity2Dao 2Dao();
public abstract Entity3Dao 3Dao();

public static AppDatabase getDatabase(Context context) {
    if (INSTANCE == null) {
        INSTANCE = createDatabase(context);
    }
    return (INSTANCE);
}

  private static AppDatabase createDatabase(Context context) {
    RoomDatabase.Builder<AppDatabase> builder =
            Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class,
                    context.getString(R.string.dbase_name));
    return (builder.openHelperFactory(new AssetSQLiteOpenHelperFactory())
            .allowMainThreadQueries()
            .build());
  }
}