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# subscriptionID

The subscription identifier for the associated database.

```
@property (copy, nullable) CKSubscriptionID subscriptionID;
```

## Discussion

By default, a sync engine attempts to discover an existing subscription for the synced database.
If one isn’t found, the engine creates an internal [`CKDatabaseSubscription`](/documentation/CloudKit/CKDatabaseSubscription) and uses that to receive notifications about remote record changes.

If you require the sync engine to use a specific database subscription, assign that subscription’s identifier to this property.
Doing so enables your app to be backwards compatible if you’re migrating to [`CKSyncEngine`](/documentation/CloudKit/CKSyncEngine-4b4w9) from a custom CloudKit sync implementation.

The default value is `nil`.

---

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