# HKAnchoredObjectQueryDescriptor A query interface that runs anchored object queries using Swift concurrency. ``` struct HKAnchoredObjectQueryDescriptor where Sample : HKSample ``` ## Overview Use [`HKAnchoredObjectQueryDescriptor`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor) to read any changes to the HealthKit store that occurred after the provided anchor. When creating a new query descriptor, if you pass `nil` as the `anchor` parameter, the query reads all matching data from the store. There are two common use cases for anchored object queries: - Batch-read all the matching data from the HealthKit store using a series of [`HKAnchoredObjectQueryDescriptor`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor) instances. - Monitor the HealthKit store for any changes to the matching data using a long-running [`HKAnchoredObjectQueryDescriptor`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor) instance. ### Batch Read Existing Data Users may have large quantities of data saved to the HealthKit store; therefore, reading all data for a given data type might become very expensive, both in terms of memory usage and processing time. To avoid performance issues, you can use [`HKAnchoredObjectQueryDescriptor`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor) queries to read the data in batches. Start with a `nil`-valued anchor, and create a one-shot query descriptor that reads a batch of data. After you process the results from one query, start a new one-shot query for the next batch. Continue reading batches until there’s no new data. ```swift let stepType = HKQuantityType(.stepCount) // Start by reading all matching data. var anchor: HKQueryAnchor? = nil var results: HKAnchoredObjectQueryDescriptor.Result repeat { // Create a query descriptor that reads a batch // of 100 matching samples. let anchorDescriptor = HKAnchoredObjectQueryDescriptor( predicates: [.quantitySample(type: stepType)], anchor: anchor, limit: 100 ) results = try await anchorDescriptor.result(for: store) anchor = results.newAnchor // Process the batch of results here. } while (results.addedSamples != []) && (results.deletedObjects != []) ``` > Tip: > Because ``doc://com.apple.healthkit/documentation/HealthKit/HKQueryAnchor`` instances adopt the protocol, you can save the most recent anchor and use it the next time your app launches. ### Monitor for Changes To monitor the HealthKit store for changes, start by creating an [`HKAnchoredObjectQueryDescriptor`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor) instance that matches the data you want to monitor. Pass in the anchor from the last time you read data from the HealthKit store. Next, call the query descriptor’s [`results(for:)`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/results(for:)) method to start your long-running query. This method returns an instance which HealthKit uses to return `Element` instances. The first result represents any changes currently in the HealthKit store, and additional results represent changes as they occur. ```swift let stepType = HKQuantityType(.stepCount) // Create a query descriptor. let anchorDescriptor = HKAnchoredObjectQueryDescriptor( predicates: [.quantitySample(type: stepType)], anchor: anchor ) let updateQueue = anchorDescriptor.results(for: store) updateTask = Task { for try await update in updateQueue { // Process the update here. print(update) } } ``` ## Topics ### Creating Query Descriptors [`init(predicates: [HKSamplePredicate], anchor: HKQueryAnchor?, limit: Int?)`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/init(predicates:anchor:limit:)) Creates an anchored object query descriptor. ### Running Queries [`func result(for: HKHealthStore) async throws -> HKAnchoredObjectQueryDescriptor.Result`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/result(for:)) Runs a one-shot query and asynchronously returns a snapshot of the current matching results. [`func results(for: HKHealthStore) -> HKAnchoredObjectQueryDescriptor.Results`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/results(for:)) Initiates a long-running query that returns its results using an asynchronous sequence. [`struct Result`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/Result) A set of results from an anchored object query. [`struct Results`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/Results) An asynchronous sequence that emits updates from an anchored object query. ### Accessing Query Properties [`var predicates: [HKSamplePredicate]`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/predicates) A predicate that limits the results that the query returns. [`var anchor: HKQueryAnchor?`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/anchor) An anchor that a previous anchored object query returned. [`var limit: Int?`](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/limit) The maximum number of samples that the query returns. ### Default Implementations [HKAsyncQuery Implementations](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/HKAsyncQuery-Implementations) [HKAsyncSequenceQuery Implementations](/documentation/HealthKit/HKAnchoredObjectQueryDescriptor/HKAsyncSequenceQuery-Implementations) ## Relationships ### Conforms To [`HKAsyncSequenceQuery`](/documentation/HealthKit/HKAsyncSequenceQuery) [`Sendable`](/documentation/Swift/Sendable) [`HKAsyncQuery`](/documentation/HealthKit/HKAsyncQuery) [`Copyable`](/documentation/Swift/Copyable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Escapable`](/documentation/Swift/Escapable) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)