MongoDB模式设计-在按用户筛选的所有博客文章中查找最后X条评论 [英] MongoDB schema design - finding the last X comments across all blog posts filtered by user

问题描述

我正在尝试使用Morphia和Play Framework将一个Post的经典博客架构重现为许多Comment.

I am trying to reproduce the classic blog schema of one Post to many Comments using Morphia and the Play Framework.

我在Mongo中的架构是:

My schema in Mongo is:

{ "_id" : ObjectId("4d941c960c68c4e20d6a9abf"), 
 "className" : "models.Post", 
  "title" : "An amazing blog post", 
  "comments" : [
    {
        "commentDate" : NumberLong("1301552278491"),
        "commenter" : {
            "$ref" : "SiteUser",
            "$id" : ObjectId("4d941c960c68c4e20c6a9abf")
        },
        "comment" : "What a blog post!"
    },
    {
        "commentDate" : NumberLong("1301552278492"),
        "commenter" : {
            "$ref" : "SiteUser",
            "$id" : ObjectId("4d941c960c68c4e20c6a9abf")
        },
        "comment" : "This is another comment"
    }
]}

我正在尝试向博客介绍社交网络方面，因此我希望能够在SiteUser的主页上提供所有帖子中该SiteUser的朋友的最后X条评论.

I am trying to introduce a social networking aspect to the blog, so I would like to be able to provide on a SiteUser's homepage the last X comments by that SiteUser's friends, across all posts.

我的模型如下:

@Entity
public class Post extends Model {

    public String title;

    @Embedded
    public List<Comment> comments;

}

@Embedded
public class Comment extends Model {

    public long commentDate;

    public String comment;

    @Reference
    public SiteUser commenter;

}

根据我已阅读的内容在其他地方，我认为我需要对数据库(其中[a, b, c]代表SiteUser s)运行以下命令:

From what I have read elsewhere, I think I need to run the following against the database (where [a, b, c] represents the SiteUsers) :

db.posts.find( { "comments.commenter" : {$in: [a, b, c]}} )

我有一个List<SiteUser>可以传递给Morphia进行过滤，但是我不知道如何

I have a List<SiteUser> to pass in to Morphia for the filtering, but I don't know how to

1. 在Morphia中为Comments.commenter在Post上设置索引
2. 实际构建以上查询

1. set up an index on Post for Comments.commenter from within Morphia
2. actually build the above query

推荐答案

1. 将@Indexes(@Index("comments.commenter"))放在Post类上，或者将@Indexed放在Comment类的commenter字段上(Morphia的Datastore.ensureIndexes()将在这些类中递归并正确创建 Post集合上的索引)

1. Either put @Indexes(@Index("comments.commenter")) on the Post class, or @Indexed on the commenter field of the Comment class (Morphia's Datastore.ensureIndexes() will recurse in the classes and correctly create the comments.commenter index on the Post collection)

我认为ds.find(Post.class, "comments.commenter in", users)可以工作，ds是Datastore，而users是您的List<SiteUser>(尽管我不使用@Reference，所以我无法确认；您可能会必须首先提取其Key的列表.)

I think ds.find(Post.class, "comments.commenter in", users) would work, ds being a Datastore and users your List<SiteUser> (I don't use @Reference though, so I can't confirm; you might have to first extract the list of their Keys).

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