多个表同一个对象房间(多语言数据库) [英] Room multiple tables same Object (multi language database)

问题描述

我正在一个android项目中工作，该项目必须在本地DB(Room)中存储一些数据.我必须提供的功能之一是将数据以不同的语言存储在本地数据库中，例如，如果我有食品信息，则该信息必须以英语，德语，法语等存储.

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.

我的数据库的结构是这样的:

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{

}

我的问题是，如何让这三个不同的表(使用不同的语言)具有相同的列，并且@Dao对象为所有它们返回一个公共(父)对象?

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?

我完全不确定这是否有可能，但是如果有人对这种情况有解决方案，请提供帮助.

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

先谢谢您了:)

推荐答案

最好的解决方案是只有一个表，而不是三个表.使用一列来区分三种语言(例如，具有en，fr和de值的language列).由于无论如何您都会重写许多现有代码，因此从三个表切换到一个表似乎并不是主要障碍.

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.

话虽这么说，为了保留现有的三表结构，将Food，FoodFr和FoodDe都从一个通用的基类(例如，BaseFood)中扩展，您可以在其中定义字段/列.

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.

对于查询，您需要让DAO处理所有四种情况(三种特定的语言表，以及一种将三种三种结果组合在一起的方法)，例如:

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;
}

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