在Objectify中合并父子实体

Question

I'm in datastore and objectify I have two Kinds 1-posts 2-comments.
Post is Parent of comment.

I want to get all posts with recent 3 comments in objectify.
I know how can I get the comments using ancestor relation. But how I combine these with posts.

ofy().load().type(Comments.Class).ancestor(parentPostKey).limit(3).list();

I already know the id of Post so getting post is also very easy

ofy().load().key(key).now();

But how can I combine these two queries in one. And get result back in single class.Something like this.

ResultClass results = // Combine query

// Foreach
results.getPost().getContent();
results.getComment().getContent();
// end Foreach

Is it possible or not ? If Not what's the alternative.

Your Suggestions Please.

Answer 1

You don't need to make comments children of Posts. That will limit you in various ways, most important being that the rate at which you'll be able to add comments to posts will be limited to about 1/second (because they will all be in the same entity group).

Instead, simply save the Key<Post> in your Comment entity:

@Entity
public class Comment {

    //...

    @Index
    Key<Post> parentPost;

    //...
}

Then simply query for all the comments that have parentPost set to a particular value:

ofy().load().type(Comment.class).filter("parentPost", postKey.getRaw()).limit(3).list();

Alternatively, you could store the Key s of the Comment entities in the Post class in a List<Key<Comment>> and then use the @Load annotation to fetch them efficiently, but you'll face the same rate-limiting problem as before.