Deta Space schema migration and rollback compatibility

Direct Answer

Deta Base is a fully schemaless key‑value store and does not provide built‑in migration or rollback tooling. The only mechanisms that keep data accessible after a rollback are those you implement in your application: migration scripts that preserve the original data layout, a schema_version field on each record, and a backup of the bucket before the change.

Confirmed Facts

• There are no platform‑level configuration flags that make a schema change automatically rollback‑safe.
• Backward‑compatible changes (adding optional keys or new fields) can be rolled back without extra effort because older code simply ignores the new data.
• Destructive changes (removing keys or changing the expected type of a value) require a dedicated rollback script or a retained copy of the pre‑migration data.
• The responsibility for rollback safety lies entirely with the developer: use feature flags, separate buckets, and explicit migration scripts.

Practical Steps for a Rollback‑Safe Migration

1. Version the data. Add a schema_version key to each record before any migration. This allows the application to detect which format a record uses.

   record = {"id": "123", "name": "Alice", "schema_version": 1}

2. Back up the bucket. Before applying the migration, export or snapshot the entire bucket. Store the copy in a separate bucket named myapp‑backup‑v1.
3. Write a forward migration script. The script should:
   • Read each record from the original bucket.
   • Transform or augment the data as needed (e.g., add a new field with a default value).
   • Write the transformed record to the same bucket, preserving the schema_version or bumping it.
   • Optionally write the original record to a new bucket if you want to keep a side‑by‑side copy.
4. Deploy the new code. Enable any feature flags that switch the application to the new data format. Verify that the application reads the transformed data correctly.
5. Test rollback in staging. Deploy the previous code version to a staging environment that points to the same bucket. Verify that the old code can read the data without errors. If the old code fails, the migration was not rollback‑safe.
6. Rollback procedure. If a regression occurs:
   • Re‑enable the old feature flag or deploy the old code.
   • Use the backup bucket to restore the original data by copying records back into the main bucket, or
   • Run a dedicated rollback script that reverts the transformation (e.g., removes added fields or re‑creates missing keys).
7. Clean up. After a successful rollback, delete the migration‑specific buckets or scripts to avoid confusion.

Missing Diagnostic Detail

Do you currently store a schema_version field in your records? If not, adding this field is the first step toward a reliable rollback path.

Key Take‑aways

• Because Deta Base is schemaless, you must manage schema evolution yourself.
• Backward‑compatible changes are safe; destructive changes need explicit rollback logic.
• Always keep a pre‑migration backup and test rollback in a non‑production environment.
• Feature flags help isolate new code paths during migration.