java - 加载的实体有父级但没有@Parent

Question

我有以下架构，使用 Objectify

@Entity
public class Book{
  @Id
  private long id;
  private Key<Page> pages;
  …

}

@Entity 
public class Page{
  @Id
  private String id;
  …

  public Page(Book book,int pageNumber){
    this.id = book.getId()+””+pageNumber;
     …
  }

}

我收到投诉

com.googlecode.objectify.LoadException: Error loading Book(1401058017250)/Page("14010580172505639445604728832"): Loaded Entity has parent but com.company.api.db.Page has no @Parent

Caused by: java.lang.IllegalStateException: Loaded Entity has parent but com.company.api.db.Page has no @Parent

我来自 Eclipse 和 Datanucleus，在该框架中代码是

@Entity
public class Book{
  @Id
  private long id;
  private List<Page> pages;
  …

}

@Entity 
public class Page{
  @Id
  private Key key;
  …

  public Page(Book book,int pageNumber){
    this.key = createKey(book.getId(),pageNumber);
     …
  }

private Key createKey(long bookId, long pageNumber) {
    Key bookKey = KeyFactory.createKey(Book.class.getSimpleName(), bookId);
    Key key = KeyFactory.createKey(bookKey, Page.class.getSimpleName(), bookId + "" + pageNumber);
    return key;
  }

}

无论它是否是最好的代码，它过去都是有效的。所以无论如何，我正在迁移到 Objectify 和 Android Studio。如何重写此架构以避免出现错误？如果有人知道答案，请复制并粘贴我的代码片段并进行适当的编辑。

Answer 1

在旧代码中，您将 bookKey 标记为父实体。在新代码中，您需要:

@Parent
Key<Book> parentBook;

您的新类(class)应该是:

@Entity
public class Book{
  @Id
  private long id;
  private List<Key<Page>> pages;
  …
}

@Entity 
public class Page{
  @Id
  private String id;
  @Parent
  Key<Book> parentBook;
  …

  public Page(long bookId, int pageNumber){
    this.id = bookId + ”” +pageNumber;
    this.parentBook = Key.create(Book.class, bookId);
     …
  }

}

在此处了解有关键和对象化的更多信息:https://code.google.com/p/objectify-appengine/wiki/Concepts#Keys