Android Room transactions across DAOs

The official documentation states that:

It is recommended to have multiple Dao classes in your codebase depending on the tables they touch.

and that one can mark a method with the Transaction annotation like that:

 @Dao
 public abstract class ProductDao {
    @Insert
     public abstract void insert(Product product);
    @Delete
     public abstract void delete(Product product);
    @Transaction
     public void insertAndDeleteInTransaction(Product newProduct, Product oldProduct) {
         // Anything inside this method runs in a single transaction.
         insert(newProduct);
         delete(oldProduct);
     }
 }

But what if a transaction spans multiple DAOs? Should I merge all DAOs into one just to support transactions, or there's a better way to do that?

You can use RoomDatabase.runInTransaction(...)

Something like:

database.runInTransaction(new Runnable(){
  @Override
  public void run(){
    Access all your daos here
  }
});