Convert jsonb comma separated values into a json object using a psql script - postgresql

Question

I have a table in postgresql that has two columns:
Table "schemaname.tablename"
Column | Type | Collation | Nullable | Default
--------+-------------------+-----------+----------+---------
_key | character varying | | not null |
value | jsonb | | |
Indexes:
"tablename_pkey" PRIMARY KEY, btree (_key)
and I'd like to convert a nested property value of the jsonb that looks like this:
{
"somekey": "[k1=v1, k2=v2, k3=v2]",
}
into this:
{
"somekey": [
"java.util.LinkedHashMap",
{
"k1": "v1",
"k2": "v2",
"k3": "v3"
}
]
}
I've managed to parse the comma separted string into an array of strings but aside from having to still apply another split on '=' I don't really know how to do the actual UPDATE on all rows of the table and generate the proper jsonb value for "somekey" key.
select regexp_split_to_array(RTRIM(LTRIM(value->>'somekey','['),']'),',') from schemaname.tablename;
Any ideas?

Answer 1

Try this one (self-contained test data):
WITH tablename (_key, value) AS (
VALUES
('test', '{"somekey":"[k1=v1, k2=v2, k3=v2]"}'::jsonb),
('second', '{"somekey":"[no one=wants to, see=me, with garbage]"}'::jsonb),
('third', '{"somekey":"[some,key=with a = in it''s value, some=more here]"}'::jsonb)
)
SELECT
tab._key,
jsonb_insert(
'{"somekey":["java.util.LinkedHashMap"]}', -- basic JSON structure
'{somekey,0}', -- path to insert after
jsonb_object( -- create a JSONB object on-the-fly from the key-value array
array_agg(key_values) -- aggregate all key-value rows into one array
),
true -- we want to insert after the matching element, not before it
) AS json_transformed
FROM
tablename AS tab,
-- the following is an implicit LATERAL join (function based on eahc row for previous table)
regexp_matches( -- produces multiple rows
btrim(tab.value->>'somekey', '[]'), -- as you started with
'(\w[^=]*)=([^,]*)', -- define regular expression groups for keys and values
'g' -- we want all key-value sets
) AS key_values
GROUP BY 1
;
...resulting in:
_key | json_transformed
--------+-------------------------------------------------------------------------------------------------------
second | {"somekey": ["java.util.LinkedHashMap", {"see": "me", "no one": "wants to"}]}
third | {"somekey": ["java.util.LinkedHashMap", {"some": "more here", "some,key": "with a = in it's value"}]}
test | {"somekey": ["java.util.LinkedHashMap", {"k1": "v1", "k2": "v2", "k3": "v2"}]}
(3 rows)
I hope the inline comments explain how it works in enough detail.
Without requiring aggregate/group by:
The following requires no grouping as we don't need aggregate function array_agg, but are a little bit less strict on the key-value format and will break a query easily because of some data (the previous variant will just drop some key-value):
WITH tablename (_key, value) AS (
VALUES
('test', '{"somekey":"[k1=v1, k2=v2, k3=v2]"}'::jsonb),
('second', '{"somekey":"[no one=wants to, see=me, with garbage]"}'::jsonb)
)
SELECT
_key,
jsonb_insert(
'{"somekey":["java.util.LinkedHashMap"]}', -- basic JSON structure
'{somekey,0}', -- path to insert after
jsonb_object( -- create a JSONB object on-the-fly from the key-value array
key_values -- take the keys + values as split using the function
),
true -- we want to insert after the matching element, not before it
) AS json_transformed
FROM
tablename AS tab,
-- the following is an implicit LATERAL join (function based on eahc row for previous table)
regexp_split_to_array( -- produces an array or keys and values: [k, v, k, v, ...]
btrim(tab.value->>'somekey', '[]'), -- as you started with
'(=|,\s*)' -- regex to match both separators
) AS key_values
;
...results into:
_key | json_transformed
--------+--------------------------------------------------------------------------------
test | {"somekey": ["java.util.LinkedHashMap", {"k1": "v1", "k2": "v2", "k3": "v2"}]}
second | {"somekey": ["java.util.LinkedHashMap", {"see": "me", "no one": "wants to"}]}
(2 rows)
Feeding it with garbage (as in the "second" row before) or with an = character in the value (as in the "third" row before) would result in the following error here:
ERROR: array must have even number of elements