json - postgresql - 查询以建立 json

Question

运行:PostgreSQL 9.6.2

我将数据以键/值对的形式存储在表中。 “key”其实就是一个json对象的路径，每一个都是一个属性。因此，例如，如果键是“cogs”、“props1”、“value”，则 json 对象将如下所示:

{
  "cogs":{
     "props1": {
       "value": 100    
      }
  }
}

如果可能的话，我想通过 SQL 查询以某种方式重建一个 json 对象。这是测试数据集:

drop table if exists test_table;
CREATE TABLE test_table
(
    id serial,
    file_id integer NOT NULL,
    key character varying[],
    value character varying,
    status character varying
)
WITH (
    OIDS = FALSE
)
TABLESPACE pg_default;

insert into test_table (file_id, key, value, status)
values (1, '{"cogs","description"}', 'some awesome cog', 'approved');
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","display"}', 'Giant Cog', null);
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","props1","value"}', '100', 'not verified');
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","props1","id"}', 26, 'approved');
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","props1","dimensions"}', '{"200", "300"}', null);
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","props2","value"}', '200', 'not verified');
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","props2","id"}', 27, 'approved');
insert into test_table (file_id, key, value, status)
values (1, '{"cogs","props2","dimensions"}', '{"700", "800"}', null);

insert into test_table (file_id, key, value, status)
values (1, '{"widgets","description"}', 'some awesome widget', 'approved');
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","display"}', 'Giant Widget', null);
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","props1","value"}', '100', 'not verified');
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","props1","id"}', 28, 'approved');
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","props1","dimensions"}', '{"200", "300"}', null);
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","props2","value"}', '200', 'not verified');
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","props2","id"}', 29, 'approved');
insert into test_table (file_id, key, value, status)
values (1, '{"widgets","props2","dimensions"}', '{"900", "1000"}', null);

我正在寻找的输出是这种格式:

{
    "cogs": {
        "description": "some awesome cog",
        "display": "Giant Cog",
        "props1": {
            "value": 100,
            "id": 26,
            "dimensions": [200, 300]
        },
        "props2": {
            "value": 200,
            "id": 27,
            "dimensions": [700, 800]
        }
    },
    "widgets": {
        "description": "some awesome widget",
        "display": "Giant Widget",
        "props1": {
            "value": 100,
            "id": 28,
            "dimensions": [200, 300]
        },
        "props2": {
            "value": 200,
            "id": 29,
            "dimensions": [900, 1000]
        }
    }
}

我面临的一些问题:

1. “值”列可以包含文本、数字和数组。无论出于何种原因，使用 knex.js 的服务器端代码将整数数组(即 [100,300])存储到 postgres 中，格式如下:{"100","300"}。我需要确保我也将其提取为整数数组。

2. 努力使这种动态成为可能。也许是一个递归过程来找出“关键”路径的深度……而不是硬编码数组查找值。

3. json_object_agg 可以很好地将属性分组到单个对象中。但是，当遇到空值时它会中断。因此，如果“key”列只有两个值(即“cogs”、“description”)，我尝试聚合一个长度为三的数组(即“cogs”、“props1”、“value”)，除非我只过滤长度为 3 的数组，否则它将中断。

4. 保留输入的顺序。下面的 @klin 解决方案很棒，让我完成了 95% 的工作。但是我没有提到还要保留顺序...

Answer 1

动态解决方案需要一些工作。

首先，我们需要一个函数来将文本数组和值转换为 jsonb 对象。

create or replace function keys_to_object(keys text[], val text)
returns jsonb language plpgsql as $$
declare
    i int;
    rslt jsonb = to_jsonb(val);
begin
    for i in select generate_subscripts(keys, 1, true) loop
        rslt := jsonb_build_object(keys[i], rslt);
    end loop;
    return rslt;
end $$;

select keys_to_object(array['key', 'subkey', 'subsub'], 'value');

              keys_to_object              
------------------------------------------
 {"key": {"subkey": {"subsub": "value"}}}
(1 row)

接下来，另一个合并 jsonb 对象的函数(参见 Merging JSONB values in PostgreSQL)。

create or replace function jsonb_merge(a jsonb, b jsonb) 
returns jsonb language sql as $$ 
select 
    jsonb_object_agg(
        coalesce(ka, kb), 
        case 
            when va isnull then vb 
            when vb isnull then va 
            when jsonb_typeof(va) <> 'object' or jsonb_typeof(vb) <> 'object' then vb 
            else jsonb_merge(va, vb) end 
        ) 
    from jsonb_each(a) e1(ka, va) 
    full join jsonb_each(b) e2(kb, vb) on ka = kb 
$$;

select jsonb_merge('{"key": {"subkey1": "value1"}}', '{"key": {"subkey2": "value2"}}');

                     jsonb_merge                     
-----------------------------------------------------
 {"key": {"subkey1": "value1", "subkey2": "value2"}}
(1 row) 

最后，让我们根据上面的函数创建一个聚合，

create aggregate jsonb_merge_agg(jsonb)
(
    sfunc = jsonb_merge,
    stype = jsonb
);

我们完成了:

select jsonb_pretty(jsonb_merge_agg(keys_to_object(key, translate(value, '{}"', '[]'))))
from test_table;

                 jsonb_pretty                 
----------------------------------------------
 {                                           +
     "cogs": {                               +
         "props1": {                         +
             "id": "26",                     +
             "value": "100",                 +
             "dimensions": "[200, 300]"      +
         },                                  +
         "props2": {                         +
             "id": "27",                     +
             "value": "200",                 +
             "dimensions": "[700, 800]"      +
         },                                  +
         "display": "Giant Cog",             +
         "description": "some awesome cog"   +
     },                                      +
     "widgets": {                            +
         "props1": {                         +
             "id": "28",                     +
             "value": "100",                 +
             "dimensions": "[200, 300]"      +
         },                                  +
         "props2": {                         +
             "id": "29",                     +
             "value": "200",                 +
             "dimensions": "[900, 1000]"     +
         },                                  +
         "display": "Giant Widget",          +
         "description": "some awesome widget"+
     }                                       +
 }
(1 row)