如何在 Postgres 中加入 jsonb 数组元素？

Question

我使用的是 Postgres 9.5，我有以下表格：

用户

id UUID
姓名文字

图片

id UUID
键文本
宽度整数
身高整数

帖子

id UUID
标题文字
author_id UUID
内容 JSONB

帖子内容如下：

[
  { "type": "text", "text": "learning pg" },
  { "type": "image", "image_id": "8f4422b4-3936-49f5-ab02-50aea5e6755f" },
  { "type": "image", "image_id": "57efc97c-b9b4-4cd5-b1e1-3539f5853835" },
  { "type": "text", "text": "pg is awesome" }
]

现在我要加入图片类型的内容，并用image_id填充它们，如：

{
  "id": "cb1267ca-b1ac-4daa-8c7e-72d4c000e9fa",
  "title": "Learning join jsonb in Postgres",
  "author_id": "deba01b7-ec58-4cc2-b3ae-7dc42e582767",
  "content": [
    { "type": "text", "text": "learning pg" },
    {
       "type": "image",
       "image": {
         "id": "8f4422b4-3936-49f5-ab02-50aea5e6755f",
         "key": "/upload/test1.jpg",
         "width": 800,
         "height": 600
       }
    },
    {
       "type": "image",
       "image": {
         "id": "57efc97c-b9b4-4cd5-b1e1-3539f5853835",
         "key": "/upload/test2.jpg",
         "width": 1280,
         "height": 720
       }
    },
    { "type": "text", "text": "pg is awesome" }
  ]
}

这是我的测试sql文件：

CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

DROP TABLE IF EXISTS Users;
DROP TABLE IF EXISTS Images;
DROP TABLE IF EXISTS Posts;

CREATE TABLE Users (
  id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
  name text NOT NULL
);

CREATE TABLE Images (
  id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
  key TEXT,
  width INTEGER,
  height INTEGER,
  creator_id UUID
);

CREATE TABLE Posts (
  id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
  title TEXT,
  author_id UUID,
  content JSONB
);


DO $$
DECLARE user_id UUID;
DECLARE image1_id UUID;
DECLARE image2_id UUID;

BEGIN

INSERT INTO Users (name) VALUES ('test user') RETURNING id INTO user_id;
INSERT INTO Images (key, width, height, creator_id) VALUES ('upload/test1.jpg', 800, 600, user_id) RETURNING id INTO image1_id;
INSERT INTO Images (key, width, height, creator_id) VALUES ('upload/test2.jpg', 600, 400, user_id) RETURNING id INTO image2_id;
INSERT INTO Posts (title, author_id, content) VALUES (
  'test post',
  user_id,
  ('[ { "type": "text", "text": "learning pg" }, { "type": "image", "image_id": "' || image1_id || '" }, { "type": "image", "image_id": "' || image2_id || '" }, { "type": "text", "text": "pg is awesome" } ]') :: JSONB
);

END $$;

有什么办法可以实现这个要求吗？

Answer 1

假设至少是 Postgres 9.5，这将完成这项工作：

SELECT jsonb_pretty(to_jsonb(p)) AS post_row_as_json
FROM  (
   SELECT id, title, author_id, c.content
   FROM   posts p
   LEFT   JOIN LATERAL (
      SELECT jsonb_agg(
               CASE WHEN c.elem->>'type' = 'image' AND i.id IS NOT NULL
                    THEN elem - 'image_id' || jsonb_build_object('image', i)
                    ELSE c.elem END) AS content
      FROM   jsonb_array_elements(p.content) AS c(elem)
      LEFT   JOIN images i ON c.elem->>'type' = 'image'
                          AND i.id = (elem->>'image_id')::uuid
      ) c ON true
   ) p;

怎么办？

取消嵌套 jsonb 数组，每个数组元素生成 1 行：
```
jsonb_array_elements(p.content) AS c(elem)
```
对于每个元素LEFT JOIN到images，条件是
一种。键 'type' 具有值 'image': c.elem->>'type' = 'image'
b. image_id 中的 UUID 匹配：i.id = (elem->>'image_id')::uuid
^{请注意，content 中的无效 UUID 会引发异常。}
对于图像类型，找到匹配图像的位置
```
c.elem->>'type' = 'image' AND i.id IS NOT NULL
```
删除键 'image_id' 并将相关图像行添加为 jsonb 值：
```
elem - 'image_id' || jsonb_build_object('image', i)
```
否则保留原始元素。
使用jsonb_agg().
将修改后的元素重新聚合到新的content列 ^{也适用于普通 ARRAY constructor。}
无条件LEFT JOIN LATERAL结果到posts和select所有列，只用生成的替换c.content替换p.content
在外部 SELECT 中，使用简单的 to_jsonb().
将整行转换为 jsonb ^{jsonb_pretty() 对于人类可读表示来说是完全可选的。}

All jsonb functions are documented in the manual here.

如何在 Postgres 中加入 jsonb 数组元素？

How to join jsonb array elements in Postgres?

sql

postgresql

json

jsonb

怎么办？