Convert JSON to CSV

Flattening is lossy, and the loss is worth naming

A CSV is a rectangle. JSON is a tree. Converting one to the other means choosing what to throw away, and every converter makes that choice silently.

Here, a nested object becomes dotted columns: {"user":{"id":7}} becomes a column named user.id. That round-trips cleanly. An array of scalars becomes a single cell with semicolon-joined values, which does not round-trip if any value contains a semicolon. An array of objects — the common case of a customer with several orders — has no rectangular representation at all, and is stringified rather than expanded into multiple rows.

If your data has one-to-many relationships, a single CSV cannot express them. The honest answer is two CSVs and a foreign key, exactly as a database would model it. Any tool that claims to flatten arrays of objects into columns is generating orders.0.total, orders.1.total and so on, and will produce a different column set for every record.