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Query Subscriptions

Skygear make it easy for you to subscribe to changes on the Database for real-time update. For example, you can create a query of all photos uploaded by a user Ben, and when the result set of query updated (for example a new photo was uploaded, or a photo uploaded by the user is deleted), your app will receive a notification.

Creating a subscription requires your application to register the current device on remote server. This is required for subscription to notify the client that a subscription is triggered.

When a subscription is triggered, remote server notifies the client through the publish-subscribe (pubsub) mechanism. It is also recommended that your application requests a remote notification through the -registerForRemoteNotifications. When a device token is available for a device, the remote server also send a remote notification through Apple Push Notification Service.

Having registered a device, your application should create a subscription by specifying a query. The container will associate the device to the subscription when you call the -saveSubscription:completionHandler: on the database.

Registering device

Please refer to Push Notification - Registering device section to register the device first.

After you have registered device, you can then create a subscription.

In the register device callback, you should then add the subscriptions.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [[[SKYContainer defaultContainer] push] registerDeviceCompletionHandler:^(NSString *deviceID, NSError *error) {
        if (error) {
            NSLog(@"Failed to register device: %@", error);
            return;
        }

        // You should put subscription creation logic in the following method
        [self addSubscriptions];
    }];

    // This will prompt the user for permission to send remote notification
    [application registerForRemoteNotifications];

    // Other application initialization logic here
}

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
    SKYContainer.default().push.registerDeviceCompletionHandler { (deviceID, error) in
        if error != nil {
            print ("Failed to register device: \(error)")
            return
        }

        // You should put subscription creationg logic in the following method
        addSubscriptions()
    }

    // This will prompt the user for permission to send remote notification
    application.registerForRemoteNotifications()

    // Other application initialization logic here
}

Register for push notifications

- (void)application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken
{
    NSLog(@"Registered for Push notifications with token: %@", deviceToken.description);
    [[[SKYContainer defaultContainer] push] registerRemoteNotificationDeviceToken:deviceToken completionHandler:^(NSString *deviceID, NSError *error) {
        if (error) {
            NSLog(@"Failed to register device token: %@", error);
            return;
        }

        // You should put subscription creation logic in the following method
        [self addSubscriptions];
    }];
}

func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
    print ("Registered for Push notifications with token: \(deviceToken.description)")
    SKYContainer.default().push.registerRemoteNotificationDeviceToken(deviceToken) { (deviceID, error) in
        if error != nil {
            print ("Failed to register device token: \(error)")
            return
        }

        // You should put subscription creation logic in the following method
        addSubscriptions()
    }
}

Adding subscription

SKYQuery *query = [[SKYQuery alloc] initWithRecordType:@"note" predicate:nil];
SKYSubscription *subscription =
[[SKYSubscription alloc] initWithQuery:query subscriptionID:@"my notes"];
[[[SKYContainer defaultContainer] privateCloudDatabase] saveSubscription:subscription
                                                       completionHandler:^(SKYSubscription *subscription, NSError *error) {
    if (error) {
        NSLog(@"Failed to subscribe for my note: %@", error);
        return;
    }

    NSLog(@"Subscription successful.");
}];

let query = SKYQuery(recordType: "note", predicate: nil)
let subscription = SKYSubscription(query: query, subscriptionID: "my notes")
SKYContainer.default().privateCloudDatabase.save(subscription) { (subscription, error) in

    if error != nil {
        print ("Failed to subscribe for my note: \(error)")
        return
    }

    print ("Subscription successful.")
}

Implementing SKYContainerDelegate to receive notification

In Objective-C, add protocol declaration in AppDelegate.

@interface AppDelegate : UIResponder <UIApplicationDelegate, SKYContainerDelegate>

In Swift, you should add an extension to the end of AppDelegate.

extension AppDelegate: SKYContainerDelegate {

}

Note: An compiler error AppDelegate does not conform to protocol SKYContainerDelegate may occur. Just ignore it. The error will be solved after adding the delegate method.

Implement the delegate method

- (void)container:(SKYContainer *)container didReceiveNotification:(SKYNotification *)notification
{
    NSLog(@"received notification = %@", notification);
    // do more with the notification (not implemented)
}

func container(_ container: SKYContainer!, didReceive notification: SKYNotification!) {
    print ("received notification = \(notification)")
    // do more with the notification (not implemented)
}

Set AppDelegate as container's delegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [SKYContainer defaultContainer].delegate = self;
    // ...
}

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    SKYContainer.default().delegate = self
    // ...
}