Android Room:将json结果转换为db对象的有效方法 [英] Android Room: Efficient way to transform json result into db object

问题描述

我有一个看起来像这样的API调用解析的POJO

I have a POJO parsed from an API call which looks like this

public class Article {

  public Long id;

  @Expose
  @SerializedName("section")
  public String section;

  @Expose
  @SerializedName("title")
  public String title;

  @Expose
  @SerializedName("topics")
  public List<String> topics;

  @Expose
  @SerializedName("media")
  public List<Media> media;
}

为了最大限度地减少冗余和重复，我正在寻找创建这样的模式

For the sake of minimizing redundancy and duplicates, I am looking to create a schema like this

@Entity(foreignKeys = { 
          @ForeignKey(entity = Article.class, parentColumns = "id", childColumns = "articleId"), 
          @ForeignKey(entity = Topic.class, parentColumns = "id", childColumns = "topicId"),
          @ForeignKey(entity = Media.class, parentColumns = "id", childColumns = "mediaId")
}
public class Articles {

    @PrimaryKey
    public Long articleId; 

    @ColumnInfo(name = "topic_id")
    public Long topicId;

    @ColumnInfo(name = "media_id")
    public Long mediaId;
}

@Entity
public class Article {
    // Left out
}

@Entity
public class Media {
    // Left out
}

如您所见，当我调用DAO方法访问数据库时，我不能只是直接传递pojo对象(除非我对此有误).我相信我需要将对象转换为与数据库实体模型匹配的对象.

As you can see, when I call the DAO methods to access the database, I can not just pass in the pojo object directly (unless I am mistaken about this). I believe I need to transform the object to one which matches the database entity model.

Android框架是否提供从POJO转换为数据库模型对象的自然方法?除了自己手动转换外，还有其他方法吗?

Does the Android Framework provide a natural way to convert from POJO to the database model object? Is there a way to do this other than manually converting it myself?

• 我知道我可以在DAO接口内的方法内实现转换.但是然后，我将不得不创建一个新对象并手动设置所有值.
• 最初，我认为类型转换器可以工作，但它们似乎可以转换单个列.

推荐答案

您要做的就是为POJO(模型类)使用 @Embedded 批注参考另一堂课.然后创建一个类型转换器类.

All you have to do is use @Embedded annotation for your POJO(Model Class) which will refer to another class. then create a type converter class.

 @Embedded(prefix = "media")
private Meida media;

@TypeConverters({TypeConvertorClass.class})
@Database(entities = {Article .class,Media.class}, version = 1, exportSchema = false)
public abstract class `DataBaseExample` extends RoomDatabase {
}


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 fromArrayLisr(ArrayList<String> list) {
        Gson gson = new Gson();
        String json = gson.toJson(list);
        return json;
    }
}


    public class TypeConvertorClass {
    @TypeConverter
    public static Media getMedia(String longId) {
        return longId== null ? null : new Meida();
    }

}
  @Entity(tableName = "Article")
    public class Article {
        @ColumnInfo (name = "article_id")
        public Long id;

        @Expose
    @SerializedName("section")
    public String section;

    @Expose
    @SerializedName("title")
    public String title;

    @Expose
    @SerializedName("topics")
    public List<String> topics;

   @Embedded(prefix = "media") // We need relation to Media table
    @Expose
    @SerializedName("media")
    public List<Media> media;
}

public class Media {
    @ColumnInfo (name = "media_id")
    public Long id;
}

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