--- title: Syncing SwiftData with a Custom Backend Using... description: iOS 27 introduces HistoryObserver in SwiftData, enabling clean one-way synchronization between a local SwiftData store and a custom backend. The tutorial walks... canonical: https://daily.dev/posts/syncing-swiftdata-with-a-custom-backend-using-historyobserver-urp1nzc7y twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Syncing SwiftData with a Custom Backend Using HistoryObserver | daily.dev og:description: iOS 27 introduces HistoryObserver in SwiftData, enabling clean one-way synchronization between a local SwiftData store and a custom backend. The tutorial walks... og:url: https://daily.dev/posts/syncing-swiftdata-with-a-custom-backend-using-historyobserver-urp1nzc7y og:image: https://api.daily.dev/og/posts/UrP1nZc7y.png og:image:alt: Syncing SwiftData with a Custom Backend Using HistoryObserver og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Syncing SwiftData with a Custom Backend Using HistoryObserver **[AzamSharp](https://daily.dev/sources/azamsharp)** · 14 min read · 0 upvotes · 0 comments ## Summary iOS 27 introduces HistoryObserver in SwiftData, enabling clean one-way synchronization between a local SwiftData store and a custom backend. The tutorial walks through building a room measurement app that detects inserts, updates, and deletes via persistent transaction history, batches changes into RoomPayload objects, and uploads them to a Node/Express REST API. Key techniques covered include tracking a lastToken bookmark to avoid reprocessing old transactions, persisting that token in UserDefaults, batching payloads for efficiency, and implementing soft deletes (marking records with isDeleted before actual removal) to ensure the server is notified before local deletion. The lastToken is only updated after a successful server response to prevent skipping unsynced changes. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Building Testable Swiftdata Apps](https://daily.dev/posts/building-testable-swiftdata-apps-e4fum1jda) · AzamSharp · 0 upvotes · 0 comments - [From Property-Level Reactivity to a Freer Mental Model](https://daily.dev/posts/from-property-level-reactivity-to-a-freer-mental-model-4zl1mw6kr) · Fatbobman · 0 upvotes · 0 comments --- Tags: [#ios](https://daily.dev/tags/ios), [#swift](https://daily.dev/tags/swift), [#offline-first](https://daily.dev/tags/offline-first) [View this post on daily.dev](https://daily.dev/posts/syncing-swiftdata-with-a-custom-backend-using-historyobserver-urp1nzc7y) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Syncing SwiftData with a Custom Backend Using HistoryObserver","url":"https://daily.dev/posts/syncing-swiftdata-with-a-custom-backend-using-historyobserver-urp1nzc7y","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/syncing-swiftdata-with-a-custom-backend-using-historyobserver-urp1nzc7y"},"datePublished":"2026-07-17T04:14:51.244Z","dateModified":"2026-07-17T04:15:12.637Z","description":"iOS 27 introduces HistoryObserver in SwiftData, enabling clean one-way synchronization between a local SwiftData store and a custom backend. 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