Convert JSON to table type
The function json_populate_record can be used to cast a JSON object to a table type:
CREATE TABLE foo(bar int);
SELECT *
FROM json_populate_record(NULL::foo, '{"bar": 42}')+-------+
| bar |
|-------|
| 42 |
+-------+This can also be used to insert into the table:
INSERT INTO foo
SELECT *
FROM json_populate_record(NULL::foo, '{"bar": 42}')