如何保存和 return JavaScript 带有归一化子数组的对象 SQL

Question

我正在使用 postgres-node，但我认为这对于拥有 javascript 对象且其子数组要保存在 SQL 中的任何人来说都是一个问题。我有一个 javascript 个具有不同数量（任意长度）特征数组的对象：

{ 
  name: "Ted",
  features: ['Red Hair', 'Blue Eyes']
}

所以当我有几个时，javascript 格式如下：

[
  { 
    name: "Ted",
    features: ['Red Hair', 'Blue Eyes']
  },
  { 
    name: "Ann",
    features: ['Brown Hair', 'Blue Eyes', 'Big Smile']
  }
]

太棒了！但是如何在规范化后从数据库中取回它呢？我已经在我的数据库中将其标准化，如下所示：

people Table

+---+------------+
|id | Name       |
+---+------------+
| 1 | Ted        |
| 2 | Ann        |
+---+------------+

features table

+---+--------------+
|id | feature_name |
+---+--------------+
| 1 | Red Hair     |
| 2 | Blue Eyes    |
| 3 | Brown Hair   |
| 4 | Big Smile    |
+---+--------------+

与people_features结table

+---+-----------+-------------+
|id | person_id | feature_id  |
+---+-----------+-------------+
| 1 | 1         | 1           |
| 2 | 1         | 2           |
| 3 | 2         | 2           |
| 4 | 2         | 3           |
| 5 | 2         | 4           |
+---+-----------+-------------+

如果我这样连接：

SELECT name, feature_name
FROM people
JOIN people_features ON people_features.person_id=people.id
JOIN features ON people_features.feature_id=features.id;

我为每个人排了一排。这不是我想要的。

我得到的：

[
  { 
    name: "Ted",
    feature_name: 'Red Hair'
  },
  { 
    name: "Ted",
    feature_name: 'Blue Eyes'
  },
  { 
    name: "Ann",
    feature_name: 'Blue Eyes'
  },
  { 
    name: "Ann",
    feature_name: 'Brown Hair'
  },
  { 
    name: "Ann",
    feature_name: 'Big Smile'
  }
]

我想要的：

[
  { 
    name: "Ted",
    features: ['Red Hair', 'Blue Eyes']
  },
  { 
    name: "Ann",
    features: ['Brown Hair', 'Blue Eyes', 'Big Smile']
  }
]

这看起来糟透了！现在我需要遍历这些并将相同的人组合成一个人对象。我的另一个选择似乎是为人民提出要求

SELECT id, name
FROM people;

哪个 return:

[
  { 
    id: 1
    name: "Ted"
  },
  { 
    id: 2
    name: "Ann"
  }
]

然后我需要循环并为每个人进行单独的 SQL 查询？

每个人：

SELECT feature_name
FROM features
JOIN people_features ON features.id=people_features.feature_id
WHERE people_features.person_id =

（$1 是我正在循环的人的 ID）

然后我会回来（给泰德）：

[
  { feature_name: 'Red Hair' },
  { feature_name: 'Blue Eyes' }
]

然后我需要从它们的对象中删除它们（只获取字符串），然后将它们添加到对象中。

其中一种是最好的方法吗？感觉他们两个都效率很低

Answer 1

应该这样做：

SELECT name, array_agg(feature_name)
FROM people
JOIN people_features ON people_features.person_id=people.id
JOIN features ON people_features.feature_id=features.id
GROUP BY people.id;

Answer 2

Vao Tsun 的回答很完美。对于那些感兴趣的人，这是我最终在我的节点代码中使用的最小版本，以使其与 node-postgres:

一起工作

var pg = require('pg');
var config = {
    user: process.env.PG_USER || null, //env var: PGUSER
    password: process.env.DATABASE_SECRET || null, //env var: PGPASSWORD
    host: process.env.DATABASE_SERVER || 'localhost', // Server hosting the postgres database
    port: process.env.DATABASE_PORT || 5432, //env var: PGPORT    
    database: process.env.DATABASE_NAME || 'lukeschlangen', //env var: PGDATABASE
    max: 10, // max number of clients in the pool
    idleTimeoutMillis: 30000, // how long a client is allowed to remain idle before being closed
};

var pool = new pg.Pool(config)

pool.connect(function (err, client, done) {
    if (err) {
        console.log('There was an error', err);
    } else {
        client.query(
            'SELECT name, array_agg(feature_name) ' +
            'FROM people ' +
            'JOIN people_features ON people_features.person_id=people.id ' +
            'JOIN features ON people_features.feature_id=features.id ' +
            'GROUP BY people.id;',
            function (err, results) {
                done();
                console.log(results.rows); // This was exactly the array I wanted
            }
        );

    }
});

如何保存和 return JavaScript 带有归一化子数组的对象 SQL

How to save and return JavaScript Object with Subarray in Normalized SQL

javascript

sql

postgresql

node-postgres