Postgresql - query to generate json
Startup: PostgreSQL 9.6.2
I have data stored in a table that is in the form of a key / value pair. The "key" is actually the path of the json object, each of which is a property. For example, if the key was "cogs", "props1", "value", then the json object would be like this:
{
"cogs":{
"props1": {
"value": 100
}
}
}
I would like to somehow restore the json object via SQL query, if possible. Here is a test case:
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);
The result I'm looking for is in this format:
{
"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]
}
}
}
Some of the problems I am facing:
-
The value column can contain text, numbers, and an array. For some reason, the server-side code using knex.js stores an array of integers (ie [100,300]) in postgres as the following format: {"100", "300"}. I need to make sure I retrieve it as an array of integers.
-
An attempt to make this dynamic as possible as possible. Maybe a recursive procedure to figure out what the depth of the "key" path exists ... rather than hardcoding values.
-
json_object_agg works well to group properties into a single object. However, it breaks when it reaches zero. So if the column "key" only has two values (ie "Cogs", "description") and I am trying to concatenate an array of length three (ie "Cogs", "props1", "value") it will break if I don't filter only arrays of length 3.
-
Save the entry order. @ Klin's solution below is amazing and gives me 95% of the way. However, I did not mention to keep order ...
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A dynamic solution takes some work.
First, we need a function to convert the text array and value to a jsonb object.
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)
Next, another function to combine jsonb objects (see Combining 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)
Finally, let's create an aggregate based on the above function,
create aggregate jsonb_merge_agg(jsonb)
(
sfunc = jsonb_merge,
stype = jsonb
);
and we ended up:
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)
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