PostgreSQL和nodejs/pg，返回嵌套的JSON [英] PostgreSQL and nodejs/pg, return nested JSON

问题描述

我正在使用带有nodejs和pg的PostgreSQL. 一切正常，但是我想从PostgreSQL作为嵌套的json输出结果-就像我在使用MongoDB或类似的东西一样.

I'm using PostgreSQL with nodejs and pg. Everything works fine, but I want to output a result from PostgreSQL as a nested json - as if I was working with MongoDB or similar.

我来自PostgreSQL的2个表是:

My 2 tables from PostgreSQL are:

portfolio (id int, name text)

cars (portfolio_id int, name text);

是否有一种正确"的方法来返回具有以下结构的JSON对象:

Is there a "correct" way of returning a JSON object with the following structure:

{
    { name: 'Portfolio #1', cars: { name: 'Car #1', name: 'Car #2' },
    { name: 'Portfolio #2', cars: { name: 'Car #3' }
}

我在nodejs/pg中查询数据库的一般方法是:

My general way of querying the database in nodejs/pg is:

client.query('SELECT ...', [params], function(err, result) {
    done();
    if (err) {
        res.status(500).json({ error: err });
    } else {
        res.json({ portfolios: result.rows });
    }
});

推荐答案

在PostgreSQL中，您可以构建以下JSON对象:

In PostgreSQL, you can build the following JSON object:

[
    { "name": "Portfolio #1", "cars": [ "Car #1", "Car #2" ] },
    { "name": "Portfolio #2", "cars": [ "Car #3" ] }
]

您可以使用以下查询从表中构造对象:

You could construct the object from your tables with the following query:

select array_to_json(array(
  select row_to_json(n)
  from portfolio p
  left join lateral (select p.name, array(select name from cars where portfolio_id = p.id) as cars) n on true
  ))

并包括cars.votes个字段:

select array_to_json(array(
  select row_to_json(n)
  from portfolio p
  left join lateral (select p.id, p.name, array_to_json(array(
     select row_to_json((select a from (select c.name, c.votes) a))
     from cars c
     where portfolio_id = p.id)) as cars) n on true
  ))

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