Postgresql 9.4 - Invalid input syntax when converting to JSONB - json

Question

I've made a simple function to update a jsonb with new values:
CREATE OR REPLACE FUNCTION jsonupdate(
IN "pJson" jsonb, IN "pNewValues" jsonb)
RETURNS jsonb AS
$BODY$
DECLARE
jsonreturn jsonb;
BEGIN
jsonreturn := (SELECT json_object_agg(keyval.key, keyval.value::jsonb)
FROM (SELECT key,
CASE WHEN "pNewValues" ? key THEN
(SELECT "pNewValues" ->> key)
ELSE
value
END
FROM jsonb_each_text("pJson")) keyval);
RETURN jsonreturn;
END; $BODY$
LANGUAGE plpgsql IMMUTABLE
COST 100;
Sample inputs and outputs:
IN: SELECT jsonupdate('{"a" : "1", "b" : "2"}', '{"a": "3"}');
OUT: {"a": 3, "b": 2}
IN: SELECT jsonupdate('{"a" : "3", "b" : { "c": "text", "d": 1 }}', '{"b": { "c": "another text" }}');
OUT: {"a": 3, "b": {"c": "another text"}}
IN: SELECT jsonupdate('{"a" : "1", "b" : "2", "c": 3, "d": 4}', '{"a": "5", "d": 6}');
OUT: {"a": 5, "b": 2, "c": 3, "d": 6}
The problem happens when using inputs like this one: SELECT jsonupdate('{"a" : "1", "b" : ""}', '{"a": "5"}') or this one: SELECT jsonupdate('{"a" : "1", "b" : "2"}', '{"a": "."}') or this one: SELECT jsonupdate('{"a" : "1", "b" : "2"}', '{"a": ""}') it gives me an error
ERROR: invalid input syntax for type json
DETAIL: The input string ended unexpectedly.
CONTEXT: JSON data, line 1:
What's wrong here?

Answer 1

You sould use the jsonb_each() function (instead of jsonb_each_text()). Also, the -> operator (instead of ->>):
CREATE OR REPLACE FUNCTION jsonupdate(IN "pJson" jsonb, IN "pNewValues" jsonb)
RETURNS jsonb
LANGUAGE sql
IMMUTABLE AS
$BODY$
SELECT json_object_agg(key, CASE
WHEN "pNewValues" ? key THEN "pNewValues" -> key
ELSE value
END)
FROM jsonb_each("pJson")
$BODY$;
jsonb_each_text() and the ->> operator converts any non-string JSON value to their string representation. Converting those back to JSON will modify your data in a way you probably don't want to.
But I have to admit, what you are trying to achieve is almost the || (concatenation) operator. I.e.
SELECT jsonb '{"a" : "1", "b" : "2"}' || jsonb '{"a": "3"}'
will give you your desired output. The only difference between || and your function is when pNewValues contains key(s), which are not in pJson: || will append those too, while your function does not append them (it only modifies existing ones).
Update: for simulating the || operator on 9.4, you can use the following function:
CREATE OR REPLACE FUNCTION jsonb_merge_objects(jsonb, jsonb)
RETURNS jsonb
LANGUAGE sql
IMMUTABLE AS
$func$
SELECT json_object_agg(key, COALESCE(b.value, a.value))
FROM jsonb_each($1) a
LEFT JOIN jsonb_each($2) b USING (key)
$func$;