Page updated Nov 10, 2023

Observe in real time

Observe model mutations in real time

You can subscribe to changes on your Models. This reacts dynamically to updates of data to the underlying Storage Engine, which could be the result of GraphQL Subscriptions as well as Queries or Mutations that run against the backing AppSync API if you are synchronizing with the cloud.

// You must hold a reference to your subscription. var postsSubscription: AmplifyAsyncThrowingSequence<MutationEvent>? // Then in the body of your code, subscribe to the subscription func subscribeToPosts() async { let postsSubscription = Amplify.DataStore.observe(Post.self) self.postsSubscription = postsSubscription do { for try await changes in postsSubscription { // handle incoming changes print("Subscription received mutation: \(changes)") } } catch { print("Subscription received error: \(error)") } } // Then, when you're finished observing, cancel the subscription func unsubscribeFromPosts() { postsSubscription?.cancel() }
1// You must hold a reference to your subscription.
2var postsSubscription: AmplifyAsyncThrowingSequence<MutationEvent>?
3
4// Then in the body of your code, subscribe to the subscription
5func subscribeToPosts() async {
6 let postsSubscription = Amplify.DataStore.observe(Post.self)
7 self.postsSubscription = postsSubscription
8
9 do {
10 for try await changes in postsSubscription {
11 // handle incoming changes
12 print("Subscription received mutation: \(changes)")
13 }
14 } catch {
15 print("Subscription received error: \(error)")
16 }
17}
18
19// Then, when you're finished observing, cancel the subscription
20func unsubscribeFromPosts() {
21 postsSubscription?.cancel()
22}

DataStore.clear() and DataStore.stop() will stop the DataStore sync engine and keep any subscriptions connected. There will not be any additional subscription events received by the subscriber until DataStore is started (DataStore.start()) or the sync engine is re-initiated upon performing a DataStore operation (query/save/delete).

This API is built on top of the Combine framework; therefore, it is only available on iOS 13 or higher.

The Amplify.Publisher.create API returns a standard AnyPublisher.

Observe query results in real-time

observeQuery(...) returns an initial data set, similar to query(...), and also automatically subscribes to subsequent changes to the query.

The first snapshot returned from observeQuery will contain the same results as calling query directly on your Model - a collection of all the locally available records. Subsequent snapshots will be emitted as updates to the dataset and received in the local store.

While data is syncing from the cloud, snapshots will contain all of the items synced so far and an isSynced status of false. When the sync process is complete, a snapshot will be emitted with all the records in the local store and an isSynced status of true.

In addition to typical real-time use cases, observeQuery can be used on app launch to show your customers an initial data set from the local store while new data is being synced from cloud.

observeQuery also accepts the same predicates and sorting options as query.

// You must hold a reference to your subscription. var postsSubscription: AmplifyAsyncThrowingSequence<DataStoreQuerySnapshot<Post>>? // Subscribe func subscribeToPosts() async { let post = Post.keys let postsSubscription = Amplify.DataStore.observeQuery( for: Post.self, where: post.title.beginsWith("post") && post.rating > 10.0, sort: .ascending(post.rating) ) // hold onto your subscription self.postsSubscription = postsSubscription do { // observe new snapshots for try await querySnapshot in postsSubscription { print("[Snapshot] item count: \(querySnapshot.items.count), isSynced: \(querySnapshot.isSynced)") } } catch { print("Error: \(error)") } } // When you're finished observing, cancel the subscription func unsubscribeFromPosts() { postsSubscription?.cancel() }
1// You must hold a reference to your subscription.
2var postsSubscription: AmplifyAsyncThrowingSequence<DataStoreQuerySnapshot<Post>>?
3
4// Subscribe
5func subscribeToPosts() async {
6 let post = Post.keys
7 let postsSubscription = Amplify.DataStore.observeQuery(
8 for: Post.self,
9 where: post.title.beginsWith("post") && post.rating > 10.0,
10 sort: .ascending(post.rating)
11 )
12 // hold onto your subscription
13 self.postsSubscription = postsSubscription
14 do {
15 // observe new snapshots
16 for try await querySnapshot in postsSubscription {
17 print("[Snapshot] item count: \(querySnapshot.items.count), isSynced: \(querySnapshot.isSynced)")
18 }
19 } catch {
20 print("Error: \(error)")
21 }
22}
23
24// When you're finished observing, cancel the subscription
25func unsubscribeFromPosts() {
26 postsSubscription?.cancel()
27}