Reset the client database on version upgrade.

    // This is the first released version of the database that implements CLIENTID. It is

    // used to identify the versions for upgrades. This should never change going forward.

    private static final int METADATA_DATABASE_VERSION_WITH_CLIENTID = 6;

    // This is the current database version. It should be updated when the database schema

    // gets updated. It is passed to the framework constructor of SQLiteOpenHelper, so

    // that's what the framework uses to track our database version.

    private static final int METADATA_DATABASE_VERSION = 6;

    // The current database version.

    private static final int CURRENT_METADATA_DATABASE_VERSION = 7;

    private final static long NOT_A_DOWNLOAD_ID = -1;

    private MetadataDbHelper(final Context context, final String clientId) {

        super(context,

                METADATA_DATABASE_NAME_STEM + (TextUtils.isEmpty(clientId) ? "" : "." + clientId),

                null, METADATA_DATABASE_VERSION);

                null, CURRENT_METADATA_DATABASE_VERSION);

        mContext = context;

        mClientId = clientId;

    }

    /**

     * Upgrade the database. Upgrade from version 3 is supported.

     * Version 3 has a DB named METADATA_DATABASE_NAME_STEM containing a table METADATA_TABLE_NAME.

     * Version 6 and above has a DB named METADATA_DATABASE_NAME_STEM containing a

     * table CLIENT_TABLE_NAME, and for each client a table called METADATA_TABLE_STEM + "." + the

     * name of the client and contains a table METADATA_TABLE_NAME.

     * For schemas, see the above create statements. The schemas have never changed so far.

     *

     * This method is called by the framework. See {@link SQLiteOpenHelper#onUpgrade}

     * @param db The database we are upgrading

     * @param oldVersion The old database version (the one on the disk)

     * @param newVersion The new database version as supplied to the constructor of SQLiteOpenHelper

     */

    @Override

    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {

        if (METADATA_DATABASE_INITIAL_VERSION == oldVersion

                && METADATA_DATABASE_VERSION_WITH_CLIENTID == newVersion) {

                && METADATA_DATABASE_VERSION_WITH_CLIENTID <= newVersion

                && CURRENT_METADATA_DATABASE_VERSION >= newVersion) {

            // Upgrade from version METADATA_DATABASE_INITIAL_VERSION to version

            // METADATA_DATABASE_VERSION_WITH_CLIENT_ID

            // Only the default database should contain the client table, so we test for mClientId.

            if (TextUtils.isEmpty(mClientId)) {

                // Only the default database should contain the client table.

                // Anyway in version 3 only the default table existed so the emptyness

                // Anyway in version 3 only the default table existed so the emptiness

                // test should always be true, but better check to be sure.

                createClientTable(db);

            }

        } else if (METADATA_DATABASE_VERSION_WITH_CLIENTID < newVersion

                && CURRENT_METADATA_DATABASE_VERSION >= newVersion) {

            // Here we drop the client table, so that all clients send us their information again.

            // The client table contains the URL to hit to update the available dictionaries list,

            // but the info about the dictionaries themselves is stored in the table called

            // METADATA_TABLE_NAME and we want to keep it, so we only drop the client table.

            db.execSQL("DROP TABLE IF EXISTS " + CLIENT_TABLE_NAME);

            // Only the default database should contain the client table, so we test for mClientId.

            if (TextUtils.isEmpty(mClientId)) {

                createClientTable(db);

            }

        } else {

            // Version 3 was the earliest version, so we should never come here. If we do, we

            // have no idea what this database is, so we'd better wipe it off.

            // If we're not in the above case, either we are upgrading from an earlier versionCode

            // and we should wipe the database, or we are handling a version we never heard about

            // (can only be a bug) so it's safer to wipe the database.

            db.execSQL("DROP TABLE IF EXISTS " + METADATA_TABLE_NAME);

            db.execSQL("DROP TABLE IF EXISTS " + CLIENT_TABLE_NAME);

            onCreate(db);