Room database migration for all

DBConstants.java

public class DBConstants {

    // word table
    public static final String TABLE_WORD = "word_table";
    public static final String KEY_WORD = "word";
    public static final String KEY_ID = "word_id";
}

DBUtils.java

public class DBUtils {
    public static ArrayList<String> getColumns(SupportSQLiteDatabase db, String tableName) {
        ArrayList<String> al = null;
        Cursor c = null;
        try {
            c = db.query("SELECT * FROM " + tableName + " LIMIT 1", null);
            if (c != null) {
                al = new ArrayList<>(Arrays.asList(c.getColumnNames()));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (c != null)
                c.close();
        }
        return al;
    }
}

Word.java

@Entity(tableName = DBConstants.TABLE_WORD)
public class Word {

    public static void upgradeWordTable(SupportSQLiteDatabase database) {

        ArrayList<String> columns = DBUtils.getColumns(database, DBConstants.TABLE_WORD);

        // 1. Create new table
        final String TABLE_NAME_TEMP = "_temp" + DBConstants.TABLE_WORD;
        database.execSQL("CREATE TABLE IF NOT EXISTS `" + TABLE_NAME_TEMP + "` (`" + DBConstants.KEY_WORD + "` TEXT NOT NULL, `" + DBConstants.KEY_ID + "` TEXT, PRIMARY KEY(`" + DBConstants.KEY_WORD + "`))");

        // 2. find common columns.
        columns.retainAll(DBUtils.getColumns(database, TABLE_NAME_TEMP));
        final String COLS = TextUtils.join(",", columns);

        // 3. Copy the data
        database.execSQL("INSERT INTO " + TABLE_NAME_TEMP + " (" + COLS + ") "
                + "SELECT " + COLS + " "
                + "FROM " + DBConstants.TABLE_WORD);

        // 4. Remove the old table
        database.execSQL("DROP TABLE " + DBConstants.TABLE_WORD);

        // 5. Change the table name to the correct one
        database.execSQL("ALTER TABLE " + TABLE_NAME_TEMP + " RENAME TO " + DBConstants.TABLE_WORD);
    }


    @PrimaryKey
    @NonNull
    @ColumnInfo(name = DBConstants.KEY_WORD)
    private String mWord;

    @Nullable
    @ColumnInfo(name = DBConstants.KEY_ID)
    private String mId;

    public Word(@NonNull String word, @Nullable String mId) {
        this.mWord = word;
        this.mId = mId;
    }

    public String getWord() {
        return this.mWord;
    }

    @NonNull
    public String getId() {
        return mId == null ? "" : mId;
    }
}

WordRoomDatabase.java

@Database(entities = {Word.class}, version = 2)
public abstract class WordRoomDatabase extends RoomDatabase {

    public abstract WordDao wordDao();

    private static WordRoomDatabase INSTANCE;


    static WordRoomDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (WordRoomDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                            WordRoomDatabase.class, "word_database")
                            .addMigrations(WordRoomDatabase.MIGRATION_1_2)
                            .build();
                }
            }
        }
        return INSTANCE;
    }

    private static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            Word.upgradeWordTable(database);
        }
    };
}