Question

运行：PostgreSQL 9.6.2

我将数据存储在一个以键/值对形式存在的表中。 “key”实际上是json对象的路径，每个对象都是一个属性。因此，例如，如果键是“cogs”，“props1”，“value”，那么json对象就是这样：

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

如果可能的话，我想以某种方式通过SQL查询重建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);

我正在寻找的输出采用以下格式：

{
    "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：

“value”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”}。我需要确保将其作为整数数组提取出来。
尽量让这种动态变得更好。也许是一个递归过程来确定存在“关键”路径的深度......而不是硬编码数组查找值。
json_object_agg可以很好地将属性组合到一个对象中。但是，当命中空值时它会中断。因此，如果“key”列只有两个值（即“cogs”，“description”），我试图聚合一个长度为3的数组（即“cogs”，“props1”，“value”），除非我只过滤长度为3的数组，否则它会破坏。
保留输入的顺序。下面的@klin解决方案非常棒，让我在那里获得95％的成功。但是我没有提到保留订购......

Answer 1

动态解决方案需要一些工作。

首先，我们需要一个函数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，让我们根据上述功能

创建聚合

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)

postgresql - 查询以构建json

1 个答案: