Coalesce value bound to object's key into parent's value - postgresql

Question

I have a PostgreSQL 12.x database. There is a column data in a table typename that contains JSON. The actual JSON data is not fixed to a particular structure; these are some examples:
{"emt": {"key": " ", "source": "INPUT"}, "id": 1, "fields": {}}
{"emt": {"key": "Stack Overflow", "source": "INPUT"}, "id": 2, "fields": {}}
{"emt": {"key": "https://www.domain.tld/index.html", "source": "INPUT"}, "description": {"key": "JSONB datatype", "source": "INPUT"}, "overlay": {"id": 5, "source": "bOv"}, "fields": {"id": 1, "description": "Themed", "recs ": "1"}}
Basically, what I'm trying to come up with is a (database migration) script that will find any object with the keys key and source, take the actual value of key and assign it to the corresponding key/value pair where the object was originally bound to. For instance:
{"emt": " ", "id": 1, "fields": {}}
{"emt": "Stack Overflow", "id": 2, "fields": {}}
{"emt": "https://www.domain.tld/index.html", "description": "JSONB datatype", "overlay": {"id": 5, "source": "bOv"}, "fields": {"id": 1, "description": "Themed", "recs ": "1"}}
I started finding the rows that contained "source": "INPUT" by using:
select * from typename
where jsonb_path_exists(data, '$.** ? (#.type() == "string" && # like_regex "INPUT")');
...but then I'm not sure how to update the returned subset or to loop through it :/

Answer 1

It took me a while but here is the update statement:
update typename
set data = jsonb_set(data, '{emt}', jsonb_extract_path(data, 'emt', 'key')::jsonb, false)
where jsonb_typeof(data -> 'emt') = 'object'
and jsonb_path_exists(data, '$.emt.key ? (#.type() == "string")')
and jsonb_path_exists(data, '$.emt.source ? (#.type() == "string" && # like_regex "INPUT")');
There are probably better ways to implement that where clause, but that one works ;)
One downside is that I had to figure it out how many keys are involved in the update and align it with the number of update statements; e.g.: in the original example there were two keys: emt and description — so it should have been two update statements.