How to get keys and values of jsonb array for a record (row) from inside PL/lpgSQL function - postgresql

Question

I have a text column in a table that contains city/country type of data, convertible to jsonb, such as:
SELECT
'{"Toronto":"Canada","Moscow":"Russia","New York":"USA"}'::text
AS city_data
and I have to convert it to a JSONB array of this format:
[
{
"city": "Moscow",
"match": false,
"country": "Russia"
},
{
"city": "Toronto",
"match": false,
"country": "Canada"
},
{
"city": "New York",
"match": false,
"country": "USA"
}
]
I am able to do it in a regular PostgreSQL query, by first getting each key/value, and then aggregating it back to JSONB array.
WITH data AS (
WITH city_table AS (
SELECT
'{"Toronto":"Canada","Moscow":"Russia","New York":"USA"}'::text AS city_data
)
SELECT cities.key AS city, cities.value AS country
FROM city_table
LEFT JOIN jsonb_each_text(city_data::jsonb) cities ON true
)
SELECT jsonb_agg(jsonb_build_object(
'city', city::text,
'country', country::text,
'match', false::boolean)) AS combined
FROM data
But I can't figure out how to do this LEFT JOIN inside a PL/pgSQL function.
The function loops over a cursor, and where a certain condition is met, I need to do this conversion and store it into a variable.
i.e. Inside cursor cur, for record rec, I have to get corresponding rec.city_data, convert it to the new format, and save it to variable var_city_data
How do I do the LEFT JOIN on a rec? Usually inside a record I just call rec.field_name and don't need to do any FROM...
I tried:
FOR rec IN cur LOOP
-- conditions........
WITH data AS (
SELECT cities.key AS city, cities.value AS country
FROM rec -- I THINK THE ERROR IS SOMEWHERE HERE AND NEXT LINE
LEFT JOIN jsonb_each_text(rec.city_data::jsonb) cities ON true
)
SELECT INTO var_city_data
jsonb_agg(jsonb_build_object('city', city::text,
'country', country::text,
'match', false::boolean))
FROM data;
RAISE NOTICE 'city_data: % ', var_city_data;
-- ... other conditions...
END LOOP;
I also tried removing FROM rec , doing directly FROM jsonb_each_text(rec.city_data::jsonb) etc and I keep getting errors of type PL/pgSQL function inline_code_block.
Any help would be greatly appreciated.
NOTE: this function has to work on PostgreSQL versions 9.6 and 11+

Answer 1

There is no need of LEFT JOIN or WITH Clause.
Simply try below query:
FOR rec IN cur LOOP
-- conditions........
SELECT jsonb_agg(jsonb_build_object(
'city', cities.key::text,
'country', cities.value::text,
'match', false::boolean))
INTO var_city_data
FROM jsonb_each_text(rec.city_data::jsonb) cities(key,value);
RAISE NOTICE 'city_data: % ', var_city_data;
-- ... other conditions...
END LOOP;
DEMO