如何在Postgres中加入jsonb数组元素？

Question

我正在使用Postgres 9.5，我有以下表格：

用户

• id UUID
• 名称TEXT

图片

• id UUID
• 关键文字
• 宽度INTEGER
• 高度INTEGER

帖子

• id UUID
• 标题文字
• author_id UUID
• 内容JSONB

帖子的内容如下：

[
  { "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" }
]

现在我想加入图像类型的内容，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 $$;

有没有办法实现这个要求？

Answer 1

假设至少Postgres 9.5，这将完成工作：

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;

怎么样？

1. unnest jsonb数组，每个数组元素产生1行：

    jsonb_array_elements(p.content) AS c(elem) 

2. 对于每个元素LEFT JOIN到images的条件
   一个。 键 'type'的值为 'image'： c.elem->>'type' = 'image'
   湾 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。}

3. 对于图像类型，找到匹配的图像

    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。

4. 使用jsonb_agg()将修改后的元素重新聚合到新的content列。
   ^{也适用于普通的ARRAY构造函数 。}

5. 无条件LEFT JOIN LATERAL将结果发布到posts并选择所有列，仅将p.content替换为生成的替换c.content

6. 在外部SELECT ，使用简单的to_jsonb()将整行转换为jsonb 。
   ^{jsonb_pretty()对于人类可读的表示来说是完全可选的。}

所有jsonb函数都在此处的手册中记录。