fvtt-data-migrations

To migrate Foundry VTT module data structures across schema versions, use a versioned, idempotent migration flow triggered by calling Migration.migrate() or reloading a world to run the ready hook. This ensures data integrity by validating old-to-new mappings and incrementing the schemaVersion correctly.

Foundry VTT data migration for embedded documents and flags is handled safely by applying schema-versioned patterns that batch updates and provide user feedback. This approach transforms data structures, renames fields, and removes deprecated data while ensuring updates run only once per world.

Trigger a Foundry VTT data migration in the browser console by calling Migration.migrate() directly. Alternatively, reloading a world runs the ready hook to initiate the migration flow, guiding you through validating data mappings and verifying schemaVersion increments.

Yes, Foundry VTT data migration supports batch updates and idempotent workflows to ensure data integrity. The migration flow runs exactly once per world, batching document updates and providing user feedback while safely moving data between storage locations.

Foundry VTT module migrations run repeatedly if the schema version is not incrementing correctly. The idempotent workflow requires validating old-to-new data mappings and ensuring the schemaVersion updates properly so the migration flow executes only once per world.