使用Java的Google App Engine中的多对多关系

本文介绍了使用Java的Google App Engine中的多对多关系的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 是否可以在Google App Engine中的对象之间建立多对多关系？ 我是GAE的新手，但仍在阅读它。编码看起来与我习惯的通常的Java编码大不相同。我已阅读入门留言板教程。那么，我可以从GAE用户处获得任何帮助/教程/视频/知识吗？ 谢谢。 解决方案关于文档，这是一个很好的开始： http://code.google.com/appengine/docs/java/overview.html 尊重 http://code.google.com/appengine/docs/java/datastore/jdo/relationships.html ： 我们可以通过在关系的两边维护键的集合来建立多对多关系。让我们将我们的示例调整为让Food跟踪认为它是最喜欢的人： Person.java p> import java.util.Set; import com.google.appengine.api.datastore.Key; // ... @Persistent 私人设置< Key> favoriteFoods; Food.java import java.util.Set; import com.google.appengine.api.datastore.Key; // ... @Persistent 私人设置< Key> foodFans; 在这个例子中，Person维护一组键值唯一标识了最喜欢的Food对象，而Food 维护一组Key值，用于唯一标识认为是最喜欢的Person 对象。使用键值对多对多进行建模时，请注意，应用程序有责任维护关系的双方： Album.java // ... public void addFavoriteFood（Food食物）{ favoriteFoods.add（food.getKey（））; food.getFoodFans（）。add（getKey（））; } public void removeFavoriteFood（food food）{ favoriteFoods.remove（food.getKey（））; food.getFoodFans（）。remove（getKey（））; } Is it possible to establish a Many-To-Many relationship between objects in Google App Engine?I am a newbie in GAE and still reading about it. The coding seems quite different from the usual Java coding I am used to. I've read the Getting Started guestbook tutorial. So, can I get any help/tutorials/videos/knowledge from GAE users??Thank you. 解决方案 About documentation this is a good start point:http://code.google.com/appengine/docs/java/overview.htmlRespect to many to many relationship from http://code.google.com/appengine/docs/java/datastore/jdo/relationships.html : We can model a many-to-many relationship by maintaining collections of keys on both sides of the relationship. Let's adjust our example to let Food keep track of the people that consider it a favorite:Person.javaimport java.util.Set;import com.google.appengine.api.datastore.Key;// ... @Persistent private Set<Key> favoriteFoods;Food.javaimport java.util.Set;import com.google.appengine.api.datastore.Key;// ... @Persistent private Set<Key> foodFans; In this example, the Person maintains a Set of Key values that uniquely identify the Food objects that are favorites, and the Food maintains a Set of Key values that uniquely identify the Person objects that consider it a favorite. When modeling a many-to-many using Key values, be aware that it is the app's responsibility to maintain both sides of the relationship:Album.java// ...public void addFavoriteFood(Food food) { favoriteFoods.add(food.getKey()); food.getFoodFans().add(getKey());}public void removeFavoriteFood(Food food) { favoriteFoods.remove(food.getKey()); food.getFoodFans().remove(getKey());} 这篇关于使用Java的Google App Engine中的多对多关系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！