mongodb 博客架构设计 [英] mongodb schema design for blogs

问题描述

您将如何为具有基于文档的数据库 (mongodb) 的类似博客的站点设计架构.该站点具有以下对象:用户、文章、评论.用户可以为文章添加评论.每个用户每条评论也只能投票一次.

我希望能够有效地执行这些查询:
1. 获取文章 A、对文章 A 的评论和每条评论的投票数
2. 获取用户 B 对所有文章的所有评论
3.获取用户B投票的所有评论

我的第一次尝试是将文章和评论放在单独的集合中，评论可以包含投票给它的用户列表.这使得查询 1 和 2 变得简单.对于 3，我添加了 Vote 集合，用于跟踪用户的投票.

有一些明显的缺点，例如复制用户投票数据和查询 1 需要两次调用数据库.有没有更好的方法?

文章{用户身份"}评论 {用户身份"，"文章_id",[用户投票]，}投票{用户身份"，"comment_id",}

解决方案

Article {"_id": "A","title": "你好世界",用户 ID":12345，"text": '我的测试文章',评论" : [{ 'text' : 'blah', 'user_id' : 654321, 'votes' : [987654]},{ 'text' : 'foo', 'user_id' : 987654, 'votes' : [12345, 654321] },...]}

这里的基本前提是我将 Comments 嵌套在 Article 中.Votes 仅适用于 Comment，因此它们已与每个 Comment 一起存储为数组.在这种情况下，我刚刚存储了 user_id.如果你想存储更多的信息(time_created等)，那么你可以投票给一个对象数组:

... 'votes' : [ { user_id : 987654, ts : 78946513 } ] ...

如何有效地执行查询:

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1. 获取文章 A、对文章 A 的评论和每条评论的投票数

db.articles.find( { _id : 'A' } )

这可以通过一个查询获得所有内容.您可能需要执行一些客户端逻辑来计算每个评论的投票数，但这非常简单.

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1. 获取用户 B 在所有文章中的所有评论

db.articles.ensureIndex( { "comments.user_id" : 1 } )db.articles.find( { "comments.user_id" : 987654 } )//返回所有文档字段

索引将允许有效地搜索文档中的评论.

目前无法仅从子数组中提取匹配项.这个查询实际上将返回所有带有该用户评论的文章.如果这可能是太多数据，您可以进行一些修剪.

db.articles.find( { "comments.user_id" : 987654 }, { "title" : 1, "comments.user_id" : 1 })

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1. 获取用户 B 投票的所有评论

db.articles.ensureIndex( { "comments.votes" : 1 } )db.articles.find({comments.votes":987654})

同样，这将返回所有文章，而不仅仅是评论.

这里需要进行权衡.返回文章似乎我们带回了太多数据.但是，当您进行查询 #3 时，您打算向用户显示什么?

如果没有评论本身，获取我投票赞成的评论" 的列表并没有多大用处.当然，如果没有文章本身(或者至少只有标题)，评论并没有多大用处.

大多数情况下，查询 #3 会演变为从 Votes 到 Comments 再到 Articles 的连接.如果是这样，那为什么不直接带回文章开始呢?

How would you design the schema for a blog-like site with document-based databases (mongodb). The site has the following objects: User, Article, Comment. User can add Comments to Article. Each User can also vote exactly once per Comment.

I want to be able to do these queries efficiently:
1. get Article A, comments on Article A and # of votes per comments
2. get all comments by User B across all articles
3. get all comments User B voted for

My first attempt is to put articles and comments in separate collections and comment can contain a list of users that voted for it. This makes query 1 and 2 simple. And for 3, I added Vote collection which keep tracks of votes by users.

There's some obvious drawback such as duplicating user vote data and query 1 will take two calls to the database. Is there a better approach?

Article {
  "user_id"
}

Comment {
   "user_id",
   "article_id",
   [user_voted],
}

Vote {
    "user_id",
    "comment_id",
}

解决方案

Article {
  "_id" : "A",
  "title" : "Hello World",
  "user_id" : 12345,
  "text" : 'My test article',

  "comments" : [
    { 'text' : 'blah', 'user_id' : 654321, 'votes' : [987654]},
    { 'text' : 'foo', 'user_id' : 987654, 'votes' : [12345, 654321] },
    ...
  ]
}

The basic premise here is that I've nested the Comments inside of the Article. The Votes only apply to a Comment, so they've been stored as an array with each Comment. In this case, I've just stored the user_id. If you want to store more information (time_created, etc.), then you can votes an array of objects:

... 'votes' : [ { user_id : 987654, ts : 78946513 } ] ...

How to perform your queries efficiently:

1. get Article A, comments on Article A and # of votes per comments

db.articles.find( { _id : 'A' } )

This gets everything with one query. You may have to do some client-side logic to count votes per comment, but this is pretty trivial.

1. get all comments by User B across all articles

db.articles.ensureIndex( { "comments.user_id" : 1 } )
db.articles.find( { "comments.user_id" : 987654 } ) // returns all document fields

The index will allow for efficiently searching the comments within a document.

There's currently no way to extract only the matches from a sub-array. This query will in fact return all of the articles with comments by that user. If this is potentially way too much data, you can do some trimming.

db.articles.find( { "comments.user_id" : 987654 }, { "title" : 1, "comments.user_id" : 1 })

1. get all comments User B voted for

db.articles.ensureIndex( { "comments.votes" : 1 } )
db.articles.find( { "comments.votes" : 987654 } )

Again, this will return all of the Articles, not just the comments.

There's a trade-off to be made here. Returning the article may seem like we're bringing back too much data. But what are you planning to display to the user when you make query #3?

Getting a list of "comments I've voted for" is not terribly useful without the comment itself. Of course the comment is not very useful without the article itself (or at least just the title).

Most of the time, query #3 devolves into a join from Votes to Comments to Articles. If that's the case, then why not just bring back the Articles to start with?

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