Having a schema most certainly does help, since you can know with certainty what shape a specific record has before retrieving it. If you have an ORM for your

Having a schema most certainly does help, since you can know with certainty what shape a specific record has before retrieving it. If you have an ORM for your schema-less database, you get roughly the same thing, but with weaker guarantees. Correct data migration requires knowledge of the schema of the data.