如何用ArrayList字段迁移房间数据库？

Question

已经创建了一个@Embedded类播放器。我想在其中添加ArrayList字段，该字段使用@TypeConverters，它在保存时将列表转换为Gson，在加载时将其转换为Gson。请告诉我如何在void migrate()
方法中请求将列表添加到Player类的现有实例中。

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

    public static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(final SupportSQLiteDatabase database) {
            database.execSQL("ALTER TABLE Save ADD COLUMN trainingPower 
        INTEGER DEFAULT 5 NOT NULL");
        }
    };
}

  public class Player
{
  @TypeConverters({AlbumsListConverter.class})
  private List<Albums> albumsList = new ArrayList();
  @Embedded(prefix="energy_")
  public Skills energy;
  public int energyCount;
  public int energyMax = 50;
  public String fameName;
  @Embedded(prefix="flow_")
  public Skills flow;
  public int imageID;
  int imagePers;
  @Embedded(prefix="mast_")
  public Skills mastering;
  @Embedded(prefix="mast2_")
  public Skills mastering2;
  private long money = 50;
  @Embedded(prefix="music_")
  public Skills music;
  private String name;
  public int ratingPosition = 1;
  public int reclameToken = 0;
  @TypeConverters({TrackListConverter.class})
  public List<Tracks> releaseList = new ArrayList();
  @TypeConverters({MessagesConverter.class})
  public List<Massages> messagesList = new ArrayList<>();
  private long reputation = 0;
  private int respect = 1;
...
}

类保存：

@Entity
public class Save
{
  @TypeConverters({ArrayConverter.class})
  public String[] AllTopicTracks;
  @Embedded
  private Player actor;
...
}

TypeConverter：

public class MessagesConverter {
    @TypeConverter
    public String fromMassagesList(List<Messages> messages)
    {
        Gson gson = new Gson();
        return gson.toJson(messages);
    }
    @TypeConverter
    public List<Messages>toMessagesList(String data)
    {
        Gson gson = new Gson();
        Type type = new TypeToken<List<Messages>>(){}.getType();
        return gson.fromJson(data,type);
    }
}

Answer 1

您似乎对多个变量使用了@embedded。如果对@embedded进行了注释，model类的变量将被视为同一个表的列。因此，对于同一类型的多个对象的情况，您应该使用typeConverter，其中对象可以在保存时转换为json字符串，然后作为对象检索。

与其制作嵌入式player，不如为player创建类型转换器并使用它。通过这样做，您不必为Player内的对象创建单独的类型转换器。