Android Room 递归关系

Question

房间可能有递归关系吗？
我有一个可以嵌套在类似这样的父/子结构中的实体

Category1
 |_________Category2
 |_________Category3
 |  |_________Category4
 |_________Category5`

我从一个从 WebService 获得的 json 复制这个结构。

这是我当前的实体:

@Entity(tableName = "categories")
public class Category
{
   @PrimaryKey
   @NonNull
   private String code;
   private String name;
   private String parentCode;
   @Relation(parentColumn = "code", entityColumn = "parentCode", entity = Category.class)
   private List<Category> childrens;
}

但在编译过程中，我得到一个 StackOverflow 错误:

Cause: java.lang.StackOverflowError at android.arch.persistence.room.processor.PojoProcessor.doProcess(PojoProcessor.kt:113) at android.arch.persistence.room.processor.PojoProcessor.access$doProcess(PojoProcessor.kt:74) at android.arch.persistence.room.processor.PojoProcessor$process$1.invoke(PojoProcessor.kt:105) at android.arch.persistence.room.processor.PojoProcessor$process$1.invoke(PojoProcessor.kt:74) at android.arch.persistence.room.processor.cache.Cache$Bucket.get(Cache.kt:46)

我知道我可以从实体中删除子项并迭代 json 以保存没有子项的每个类别，然后在单独的查询中通过父代码获取子项，但我只想知道是否可以递归与代码中的关系类似

Answer 1

简短的回答:不，你不能有递归关系。

长答案:
阅读房间里的关系文档 https://developer.android.com/reference/android/arch/persistence/room/Relation我发现您不能在注释为@Entity 的类中使用@Relation 注释

Note that @Relation annotation can be used only in Pojo classes, an Entity class cannot have relations. This is a design decision to avoid common pitfalls in Entity setups. You can read more about it in the main Room documentation. When loading data, you can simply work around this limitation by creating Pojo classes that extend the Entity.