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Source Code

Refer to the powersync-swift repo on GitHub

API Reference

Full API reference for the SDK

Example Projects

Gallery of example projects/demo apps built with PowerSync and Swift

Changelog

Changelog for the SDK
Up to v1.13, the Swift SDK wrapped a PowerSync Kotlin XCFramework behind Swift protocols.From v1.14, the SDK has no Kotlin dependency. It is implemented natively in Swift and uses our Rust core for the sync protocol and SQLite extension.

SDK Features

  • Real-time streaming of database changes: Changes made by one user are instantly streamed to all other users with access to that data. This keeps clients automatically in sync without manual polling or refresh logic.
  • Direct access to a local SQLite database: Data is stored locally, so apps can read and write instantly without network calls. This enables offline support and faster user interactions.
  • Asynchronous background execution: The SDK performs database operations in the background to avoid blocking the application’s main thread. This means that apps stay responsive, even during heavy data activity.
  • Query subscriptions for live updates: The SDK supports query subscriptions that automatically push real-time updates to client applications as data changes, keeping your UI reactive and up to date.
  • Automatic schema management: PowerSync syncs schemaless data and applies a client-defined schema using SQLite views. This architecture means that PowerSync SDKs handle schema changes without explicit migrations on the client side.

Installation

You can add the PowerSync Swift package to your project using either Package.swift or Xcode:

Getting Started

Prerequisites: Before you start, connect your source database to the PowerSync Service and deploy Sync Streams. These are steps 1-4 in the Setup Guide.

1. Define the Client-Side Schema

The client-side schema defines the tables and columns of the SQLite database that the PowerSync client SDK manages and that your app reads from and writes to. It is usually derived from your backend database schema and your Sync Streams, and it can also include local-only tables. You apply the schema when you instantiate the database in the next step. Schema migrations are not required. The SDK syncs schemaless data and applies the schema to that data with SQLite views. The exception is raw tables, which you create and migrate yourself.
Generate schema automaticallyIn the PowerSync Dashboard, select your project and instance and click the Connect button in the top bar to generate the client-side schema in your preferred language. The schema is generated from your Sync Streams. The CLI offers the same function.The generated schema does not include an id column. The client SDK creates an id column of type text automatically, so you do not need to declare it. See Client ID for details.
The available column types are text, integer, and real. These should match the values produced by your Sync Streams. If a value does not match, it is cast automatically. For details on how source database types map to SQLite types, see Types. Example:
You do not need to declare an id column. PowerSync creates it automatically.

2. Instantiate the PowerSync Database

Next, instantiate the PowerSync database. PowerSync streams changes from your backend source database into the client-side SQLite database, based on your Sync Streams. Your app reads from and writes to this local database whether the user is online or offline. Example:

3. Integrate with Your Backend

The backend connector connects the PowerSync client SDK to your application backend. The SDK uses it to:
  1. Get an auth token to connect to the PowerSync instance.
  2. Upload client-side writes to your backend API. The SDK places every write to the SQLite database in an upload queue and uploads the queue to your backend when the user is connected. Your backend then applies the changes to the source database.
The connector must implement two methods:
  1. PowerSyncBackendConnectorProtocol.fetchCredentials - The SDK calls this method to get authentication credentials. It caches the credentials and calls the method again only when needed, for example on the first connection or when the token is near expiry. See When fetchCredentials() is Called for details and Authentication Setup for how to generate credentials.
  2. PowerSyncBackendConnectorProtocol.uploadData - The SDK calls this method whenever it has client-side writes to upload to your backend API. Implement how those writes are processed and uploaded. See When uploadData() is Called for triggers, throttling, and retry behavior, and Writing Client Changes for the app backend implementation.
Example:
Connect the PowerSync database to sync data with your backend:
This section assumes that you use PowerSync to sync your backend source database with SQLite in your app. To manage a local SQLite database without sync, instantiate the PowerSync database without calling connect() and see the Local-Only guide.

4. Subscribe to Sync Streams

Streams defined with auto_subscribe: true start syncing as soon as the client connects. For all other streams, your app must subscribe before their data downloads. The basic pattern is: subscribe to a stream, wait for its data to sync, then unsubscribe when the data is no longer needed.
After you unsubscribe, the synced data stays in the local database for the stream’s time-to-live (TTL), which is 24 hours by default. If the app subscribes again within that time, the data is already available. See Client-Side Usage for framework hooks, per-subscription sync status, custom TTLs, priority overrides, and connection parameters.

Using PowerSync: CRUD Functions

Once the PowerSync database is connected and your streams have synced, the data is in the local SQLite database. The most commonly used CRUD functions to interact with your SQLite data are:

Fetching a Single Item (PowerSync.get / PowerSync.getOptional)

The get method executes a read-only (SELECT) query and returns a single result. It throws an exception if no result is found. Use getOptional to return a single optional result (returns nil if no result is found).

Querying Items (PowerSync.getAll)

The getAll method executes a read-only (SELECT) query and returns a set of rows.

Watching Queries (PowerSync.watch)

The watch method executes a read query whenever a change to a dependent table is made.

Mutations (PowerSync.execute)

The execute method executes a write query (INSERT, UPDATE, DELETE) and returns the results (if any).

Configure Logging

You can supply your own logger. It must conform to the LoggerProtocol:
The DefaultLogger supports the following severity levels: .debug, .info, .warn, .error.

App Groups and App Extensions

By default, the Swift SDK stores databases in applicationSupportDirectory. If you want to share local databases between multiple apps in an app group, provide an absolute path (starting with /) as dbFilename when calling PowerSyncDatabase. The path should point towards a file in the app group’s shared container.
Support for app groups and extensions was added in version 1.15, and is experimental.
With app groups and extensions, multiple processes might access the database at the same time. SQLite uses shared memory and file locking to make this safe, but there are still concerns that aren’t relevant when the database is only accessed from a single context:
  1. Concurrent writes to the database are not allowed. Within a process, the PowerSync SDK uses Swift actors to schedule writes. Outside of SQLite using file locks, there is no additional coordination for multi-process access.
    • Consider using PRAGMA busy_timeout to make SQLite wait longer.
    • Be ready to handle SQLITE_BUSY errors if multiple processes attempt to write to the database.
  2. Do not call connect() in more than one process: If two processes attempt to connect to the PowerSync Service for the same database, this wastes resources and can also lead to concurrency issues. If you share databases with extensions or app groups, ensure there is only one context responsible for connecting.
  3. Avoid multiple versions of the Swift SDK: While the SQLite file format is stable and databases can safely be accessed from multiple processes using their own SQLite version, the PowerSync SDK is not designed with this in mind. In particular, opening the same database file from multiple processes can cause PowerSync-internal migrations to get reverted. This is not a concern for app extensions released as part of the same bundle, but something to be aware of for app groups.

Custom HTTP Clients and Headers

PowerSync uses a streaming HTTP response to connect to the PowerSync Service. By default, the Swift SDK uses URLSession.shared to run HTTP requests. You can provide a custom URLSession as a sync option. This can be used to add custom HTTP headers, for example:
For more information, see Apple’s documentation on URLSessionConfiguration.

Additional Usage Examples

For more usage examples including accessing connection status, monitoring sync progress, and waiting for initial sync, see the Usage Examples page.

ORM Support

PowerSync officially supports the GRDB library for Swift. Additionally, Asier G. Morato contributed a Swift Data integration for PowerSync, allowing Swift Data models to be persisted and synced through a PowerSync database. The integration is community-owned and not officially supported by PowerSync.

Troubleshooting

See Troubleshooting for pointers to debug common issues.

Supported Platforms

See Supported Platforms -> Swift SDK.

Upgrading the SDK

Update the version number in Package.swift or via Xcode Package Dependencies as documented in the installation instructions: Installation.
Upgrading to v1.14: This release removes the internal Kotlin dependency and re-implements the SQLite connection pool logic natively in Swift. The public API is unchanged, but the internals are a full rewrite. We recommend testing queries in your app after upgrading to this version.