Room TypeConverter

问题

I am not sure what is the fuss about Room as I find it very crappy. Almost nothing works as expected. To my issue I want to test the type converter thingy they have (so far disappointed). To test it I made a simple class from an example I saw online. I am sure it is something stupid not even related to the code but I will give it a try here anyway. So far I have:

@Entity
public class User {

    @PrimaryKey
    private int id;

    private String name;

    @TypeConverters(Converters.class)
    List<String> pets = new ArrayList<>();

    public User() { }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<String> getPets() {
        return pets;
    }

    public void setPets(List<String> pets) {
        this.pets = pets;
    }
}

Then the converter:

public class Converters {
    @TypeConverter
    public static ArrayList<String> fromString(String value) {
        Type listType = new TypeToken<ArrayList<String>>() {}.getType();
        return new Gson().fromJson(value, listType);
    }
    @TypeConverter
    public static String fromArrayList(ArrayList<String> list) {
        Gson gson = new Gson();
        String json = gson.toJson(list);
        return json;
    }
}

A simple dao:

@Dao
public interface UserDao {

    @Insert(onConflict = REPLACE)
    void insertUser(User user);

    @Query("SELECT * FROM User")
    List<User> getUsers();
}

And finally the db:

@Database(entities = { User.class,}, version = 1, exportSchema = false)
@TypeConverters({Converters.class})
public abstract class RoomDb extends RoomDatabase {

    public abstract UserDao userDao();

}

And still I get "Cannot figure out how to save this field into database. You can consider adding a type converter for it" shit. No details why the converter is not working or what's so ever. To save the trouble I already tried to use the @Converters on the field it self like the alternative solution suggests.

Room has left me with disappointment so far for complicated problems, and I find Realm and ObjectBox to be more consistent when your model is fairly complicated.

Feel free to join the struggle with your insight.

回答1:

Instead of ArrayList in the Converters class. Try List. Your entity is using List as its declared class. There might be a problem with that.

That was the solution as suggested from Knossos above. I ended up testing it with ArrayList and worked.

回答2:

class Convertes {

    @TypeConverter
    fun fromSource(source: Source) :String{
        return source.name
    }
    @TypeConverter
    fun  tvSource(name: String): Source {
        return Source( name,name)
    }
}

来源：https://stackoverflow.com/questions/53085704/room-typeconverter