How to use Realm SDK with iOS App Extensions?

[matthewmorek]

I am developing an app that has a second App Target, an iOS Share Extension, which allows users to add website links to a database (Mongo Atlas) and I use Realm Swift SDK for the main app.

Due to the containerisation of app targets, my main app and the bundled iOS Share Extension use a shared App Group container and can share Realm configuration this way successfully.

Questions

• How do I share local database file between main app and share extension via App Group?
• How do I extend the user session between iOS App and Share Extension in a secure way? What would be the best strategy?
  1. Share auth details/keys via iOS Keychain (App Group) and re-authenticate via SDK (would it be possible?), add data locally, sync via Realm SDK (device → cloud)
  2. Share auth details/keys/userId via iOS Keychain (App Group) and add data via Atlas REST API, sync via Realm SDK (cloud → device)
• Do I need to notify the main app/realm that changes have been made in order for them to be synced, or is Realm SDK going to do it automatically from the Share Extension?

Thanks in advance for help

[AyoubTadlaoui]

To share Realm data between your main app and extensions (widgets, intents, etc.), you need to configure a shared App   
Group:                                                                                                                  
                                                                                                                        
### 1. Enable App Groups                                                                                                
In Xcode, for both your main app AND extension targets:                                                                 
- Signing & Capabilities → + Capability → App Groups                                                                    
- Create group: `group.com.yourcompany.yourapp`                                                                         
                                                                                                                        
### 2. Configure Shared Realm Path                                                                                      
                                                                                                                        
```swift                                                                                                                
// Shared configuration for both app and extension                                                                      
struct RealmConfig {                                                                                                    
    static var shared: Realm.Configuration {                                                                            
        let containerURL = FileManager.default                                                                          
            .containerURL(forSecurityApplicationGroupIdentifier: "group.com.yourcompany.yourapp")!                      
        let realmURL = containerURL.appendingPathComponent("shared.realm")                                              
                                                                                                                        
        var config = Realm.Configuration()                                                                              
        config.fileURL = realmURL                                                                                       
        config.schemaVersion = 1                                                                                        
        return config                                                                                                   
    }                                                                                                                   
}                                                                                                                       
                                                                                                                        
// Usage in main app                                                                                                    
let realm = try! Realm(configuration: RealmConfig.shared)                                                               
                                                                                                                        
// Usage in widget/extension - same config                                                                              
let realm = try! Realm(configuration: RealmConfig.shared)                                                               
                                                                                                                        
3. Handle Concurrent Access                                                                                             
                                                                                                                        
Extensions and main app can run simultaneously. Use realm.refresh() in your extension:                                  
                                                                                                                        
// In widget timeline provider                                                                                          
func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> Void) {                                
    let realm = try! Realm(configuration: RealmConfig.shared)                                                           
    realm.refresh() // Get latest data from main app                                                                    
                                                                                                                        
    let data = realm.objects(MyModel.self)                                                                              
    // Build timeline...                                                                                                
}                                                                                                                       
                                                                                                                        
Important Notes:                                                                                                        
                                                                                                                        
- Keep extension Realm usage lightweight (extensions have memory limits)                                                
- Consider using Realm.Configuration.readOnly = true in extensions if you only read data                                
- Schema must match between app and extension - share your model files