Room multiple tables same Object (multi language database)

Question

I am working on an android project where have to store some data in the local DB (Room). One of the functionality which I have to provide is to store the data in the local DB in different languages, for example if I have information for food, this information has to be stored in English, German, French and so on.

The structure of my DB is something like that:

@Entity(tableName = "food")
public class Food{

}

@Entity(tableName = "food_fr")
public class FoodFr{

}

@Entity(tableName = "food_de")
public class FoodDe{

}

My question is how I can have these three different tables (on different languages) with same columns and the @Dao object return one common (parent) object for all of them?

I am not really sure that is possible at all, but if someone has a solution for that case, please help.

Thanks in advance :)

Answer 1

The best solution is to have a single table, rather than three tables. Use a column to distinguish between the three languages (e.g., a language column with en, fr, and de values). Since you will be rewriting much of your existing code anyway, switching from three tables to one would not seem to be a major impediment.

That being said, to keep your existing three-table structure, have Food, FoodFr, and FoodDe all extend from a common base class (e.g., BaseFood), where you define your fields/columns.

For queries, you would need to have your DAO handle all four cases (three specific language tables, plus a method to combine the results for all three), such as:

@Query("SELECT * FROM Food")
List<Food> getAllFood();

@Query("SELECT * FROM FoodFr")
List<FoodFr> getAllFrenchFood();

@Query("SELECT * FROM FoodDe")
List<FoodDe> getAllGermanFood();

@Transaction
List<BaseFood> getAllFoodAcrossAllThreeLanguages() {
  ArrayList<BaseFood> result=new ArrayList<>();

  result.addAll(getAllFood());
  result.addAll(getAllFrenchFood());
  result.addAll(getAllGermanFood());

  return result;
}

Answer 2

You can merge different tables with @Embedded annotation. https://developer.android.com/reference/android/arch/persistence/room/Embedded?authuser=4

And in Dao class write a sql query that merge your tables with inner join and return that merged object.

You can look at my example application. https://github.com/volkansahin45/Moneycim

In Model/Pojo folder there is a Spending class and in Model/Dao folder there is SpendingDao class