Android room persistent library - How to change database version

Question

Im not clear on how to use room after i have updated the database version.

For example, lets say i originally had the following database defined in room:

@Database(entities = {Event.class}, version = 1)
@TypeConverters(DateTypeConverter.class)
public abstract class EventDatabase extends RoomDatabase {

   public abstract EventDao eventDao();

}

and then i change the version so that it looks like this now:

@Database(entities = {Event.class}, version = 2)
@TypeConverters(DateTypeConverter.class)
public abstract class EventDatabase extends RoomDatabase {

   public abstract EventDao eventDao();

}

when i saw change the version i mean that i may have added or deleted columns in the database so its not same. my questions are the following:

do i need to maintain two databases now ? v1 and v2 ? and is there a way to copy entities easily over to v2 ? also when changing the version is it enough to simply change it from 1 to 2 or do i have to create another class called EventDatabase2 for example ?

also here is the version of room i am using:android.arch.persistence.room:runtime:1.0.0-alpha1

Answer 1

So lets say i have a new app version and a new database version also. I simply need to change the version = 2 like this:

@Database(entities = {Event.class}, version = 2)
@TypeConverters(DateTypeConverter.class)
public abstract class EventDatabase extends RoomDatabase {

   public abstract EventDao eventDao();

}

and then provide a migration policy like this:

Room.databaseBuilder(getApplicationContext(), MyDb.class, "database-name")
        .addMigrations(MIGRATION_1_2).build();

static final Migration MIGRATION_1_2 = new Migration(1, 2) {
    @Override
    public void migrate(SupportSQLiteDatabase database) {
        database.execSQL("CREATE TABLE `Fruit` (`id` INTEGER, "
                + "`name` TEXT, PRIMARY KEY(`id`))");
    }
};

the key thing here is if a migration policy is not provided it seem the entire database is rebuilt (so your user would loose all previous data).

this is according to @commonsWare update link provided .