从SQL hasmany关系构造嵌套对象图 [英] Construct nested object graph from SQL hasmany relationship

问题描述

示例：我有一些文章和评论，我想得到这样的东西：

Example: I have some articles and comments and I want to get something like this:

[{
   title: "Article 1",
   content: "Super long article goes here",
   comments: [
      { author: "Troll", message: "You suck, Sir!" }, 
      { author: "SpamBot", message: "http://superawesomething.com/"}
   ]
},{
   title: "Article 2",
   content: "Another long article goes here",
   comments: [ ... ]
}]

现在我看到两个解决方案：

Right now I see two solutions:

1. 首先获取文章，然后在第二个查询中添加评论并具有一些 IN 条件，最后将注释添加到相应的文章中。


2. 好的旧联接。对于我来说，我仍然不得不花很多时间处理数据才能进入我想要的结构。但除此之外，我有点担心，因为对于每个评论，都会传输诸如 articles.content 之类的有效负载-除非有一种我不知道的连接方式。

1. Get the articles first, then the comments in a second query with some IN condition and finally add the comments to the respective articles.
2. Good old joins. For one I will still have to fiddle around with the data a lot to get into the structure I want. But beyond that I'm a little concerned since payload like articles.content will be transmitted for every comment - unless there is a way to do the join I am not aware of.

我希望我的SQL文盲让我错过了简单的解决方案。

I'm hoping that my SQL-illiteracy makes me miss the simple solution.

推荐答案

您可以使用聚合和/或子查询来做到这一点。像这样的东西：

You can do this, using aggregates and/or subqueries. Something like:

select title, content, json_agg(comments.author, comments.message) as comments
from articles 
join comments on articles.article_id = comments.article_id
group by article_id;

如果您需要将其汇总成一个字符串/ json /某物-只需将其包装到另一个汇总查询中即可

If you need this aggregated into one string/json/something - just wrap it into another aggregate query like this:

select json_agg(sub)
from (
  select title, content, json_agg(comments.author, comments.message) as comments
  from articles 
  join comments on articles.article_id = comments.article_id
  group by article_id) sub;

这是一个Postgres查询。对Mysql没有经验。

This is a Postgres query. Have no expirience with Mysql.

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