PostgreSQL function to produce diff of two jsonb objects. Does not support arrays.

jsonb_diff.sql

--
-- Helper function to produce a diff of two jsonb values.
--
-- Accepts:
--   val1: original jsonb value
--   val2: updated jsonb value
--
-- Returns:
--   jsonb of changed values
--
-- Examples:
--   val1:     {"a": {"b": 1}}
--   val2:     {"a": {"b": 1, "c": 2}}
--   returns:  {"a": {"c": 2}}
--

create or replace function jsonb_diff
  (old jsonb, new jsonb)
  returns jsonb
  language 'plpgsql'
as
$$
declare
  result        jsonb;
  object_result jsonb;
  k             text;
  v             record;
  empty         jsonb = '{}'::jsonb;
begin
  if old is null or jsonb_typeof(old) = 'null'
    then
      return new;
  end if;

  if new is null or jsonb_typeof(new) = 'null'
    then
      return empty;
  end if;

  result = old;

  for k in select * from jsonb_object_keys(old)
    loop
      result = result || jsonb_build_object(k, null);
    end loop;

  for v in select * from jsonb_each(new)
    loop
      if jsonb_typeof(old -> v.key) = 'object' and jsonb_typeof(new -> v.key) = 'object'
        then
          object_result = audit_public.jsonb_diff(old -> v.key, new -> v.key);
          if object_result = empty
            then
              result = result - v.key;
            else
              result = result || jsonb_build_object(v.key, object_result);
          end if;
        elsif old -> v.key = new -> v.key
          then
            result = result - v.key;
        else
          result = result || jsonb_build_object(v.key, v.value);
      end if;
    end loop;

  return result;

end;
$$;