Postgres: transform json object into array of key-value pairs - json

Question

With this select:
SELECT '{"key1": "value1", "key2": "value2"}'::jsonb
can we transform the result object into the following array of objects keeping their keys and values respectively?
[{"key1": "value1"}, {"key2": "value2"}]
In my case, I have many-2-many relationship of tags and operations, and the following query with aggregation of tags into json object for each operation:
SELECT ot.operation_id, json_object_agg(t.name, t.value) AS tagsjson
FROM tag t
INNER JOIN operation_tag ot ON t.tag_id = ot.tag_id
GROUP BY ot.operation_id
This works fine except format of the result: I need array of tags [{name : value},...] instead of whole object containing tags as it's properties:

Answer 1

If I understand you correctly you are in a situation like the following:
your source table contains id, keys and values like the below
create table test_k_v (id int, k varchar, v varchar);
insert into test_k_v values (1, 'key1', 'value1');
insert into test_k_v values (1, 'key2', 'value2');
insert into test_k_v values (2, 'key3', 'value3');
insert into test_k_v values (2, 'key4', 'value4');
insert into test_k_v values (2, 'key5', 'value5');
which results in
defaultdb=> select * from test_k_v;
id | k | v
----+------+--------
1 | key1 | value1
1 | key2 | value2
2 | key3 | value3
2 | key4 | value4
2 | key5 | value5
(5 rows)
If so, you can create an array with all the tags with the following query:
select id, array_agg(json_build_object(k, v)) agg_res
from test_k_v
group by id;
result
id | agg_res
----+---------------------------------------------------------------------------------
2 | {"{\"key3\" : \"value3\"}","{\"key4\" : \"value4\"}","{\"key5\" : \"value5\"}"}
1 | {"{\"key1\" : \"value1\"}","{\"key2\" : \"value2\"}"}
(2 rows)