I'm building [ mongopg-migrate ], a tool that migrates MongoDB collections onto an existing Postgres schema you already designed. It's alpha pip install mongopg-migrate , currently v0.2.0. This is a bug from it, the worst one I've hit so far, because every safeguard the tool has fired correctly, and the migration still came out wrong. The setup The tool supports nested arrays ( explode: ): a Mongo array becomes a child table, and an array inside that array becomes a grandchild...