android - SQLiteOpenHelper problem with fully qualified DB path name

Question

In my app, I use...

myFilesDir = new File(Environment.getExternalStorageDirectory().getAbsolutePath()
                      + "/Android/data/" + packageName + "/files");
myFilesDir.mkdirs();

This is fine and the resulting path is...

/mnt/sdcard/Android/data/com.mycompany.myApp/files

I need a SQLite DB which I want to store on the SD card so I extend SQLiteOpenHelper as follows...

public class myDbHelper extends SQLiteOpenHelper {

    public myDbHelper(Context context, String name, CursorFactory factory, int version) {
        // NOTE I prefix the full path of my files directory to 'name'
        super(context, myFilesDir + "/" + name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // Create tables and populate with default data...
    }
}

So far so good - the first time I call getReadableDatabase() or getWriteableDatabase() the empty DB is created on the SD card and onCreate() populates it.

So here's the problem - the app is in beta testing with maybe 5 or 6 people and, like me, they're running Android v2.2 and everything works fine. I have one tester, however, running v2.1 and when myDbHelper tries to create the DB on first use, it crashes with the following...

E/AndroidRuntime( 3941): Caused by: java.lang.IllegalArgumentException: File /nand/Android/data/com.mycompany.myApp/files/myApp-DB.db3 contains a path separator
E/AndroidRuntime( 3941): at android.app.ApplicationContext.makeFilename(ApplicationContext.java:1445)
E/AndroidRuntime( 3941): at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:473)
E/AndroidRuntime( 3941): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193)
E/AndroidRuntime( 3941): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
E/AndroidRuntime( 3941): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158)

The path for the files directory is an odd one ("/nand") as it's internal memory although not the phone's own internal memory - but it is the path returned by getExternalStorageDirectory() for this device.

I can see three possible answers...

1. Although acceptable on v2.2, specifying a fully qualified path for DB name isn't recommended and will fail on earlier versions
2. Fully qualified paths are acceptable for SD card storage but the "/nand" path is being interpreted as 'internal' and only relative paths are acceptable in this case
3. Something else which I'm missing completely

If any or all of the above apply I'd appreciate it if somebody could help with how I should approach this.

Thanks.

Answer 1

You can use the SQLiteOpenHelper with a custom path if you provide a custom ContextClass and if you have write access in the target directory.

public class DatabaseHelper extends SQLiteOpenHelper {
  private static final int DATABASE_VERSION = 3;
    .....

  DatabaseHelper(final Context context, String databaseName)  {
    super(new DatabaseContext(context), databaseName, null, DATABASE_VERSION);
  }
}

And here is the custom DatabaseContext class that does all the magic:

class DatabaseContext extends ContextWrapper {

  private static final String DEBUG_CONTEXT = "DatabaseContext";

  public DatabaseContext(Context base) {
    super(base);
  }

  @Override
  public File getDatabasePath(String name)  {
    File sdcard = Environment.getExternalStorageDirectory();    
    String dbfile = sdcard.getAbsolutePath() + File.separator+ "databases" + File.separator + name;
    if (!dbfile.endsWith(".db")) {
      dbfile += ".db" ;
    }

    File result = new File(dbfile);

    if (!result.getParentFile().exists()) {
      result.getParentFile().mkdirs();
    }

    if (Log.isLoggable(DEBUG_CONTEXT, Log.WARN)) {
      Log.w(DEBUG_CONTEXT, "getDatabasePath(" + name + ") = " + result.getAbsolutePath());
    }

    return result;
  }

  /* this version is called for android devices >= api-11. thank to @damccull for fixing this. */
  @Override
  public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory, DatabaseErrorHandler errorHandler) {
    return openOrCreateDatabase(name,mode, factory);
  }

  /* this version is called for android devices < api-11 */
  @Override
  public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {
    SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), null);
    // SQLiteDatabase result = super.openOrCreateDatabase(name, mode, factory);
    if (Log.isLoggable(DEBUG_CONTEXT, Log.WARN)) {
      Log.w(DEBUG_CONTEXT, "openOrCreateDatabase(" + name + ",,) = " + result.getPath());
    }
    return result;
  }
}

Update june 2012:
how does this work (@barry question):

Normal android apps have their local database files relative to the app folder. By using a customer context with overwritten getDatabasePath() the database is now relative to a different directory on the sd card.

Update feb 2015:
After replacing my old android-2.2 device with a new android-4.4 device I found out that my solution didn't work anymore. Thanks to @damccull-s answer I was able to fix it. I have updated this answer so this should be a working example again.

Update may 2017:

Statistics: This aproach is used in more than 200 github projects