Initializing the Amazon Cognito Sync client Understanding datasets Reading and writing data in datasets Synchronizing local data with the sync store

Synchronizing data across clients

If you're new to Amazon Cognito Sync, use AWS AppSync. Like Amazon Cognito Sync, AWS AppSync is a service for synchronizing application data across devices.

It enables user data like app preferences or game state to be synchronized. It also extends these capabilities by allowing multiple users to synchronize and collaborate in real time on shared data.

With Amazon Cognito, you can save user data in datasets that contain key-value pairs. Amazon Cognito associates this data with an identity in your identity pool so that your app can access it across logins and devices. To sync this data between the Amazon Cognito service and an end user’s devices, invoke the synchronize method. Each dataset can have a maximum size of 1 MB. You can associate up to 20 datasets with an identity.

The Amazon Cognito Sync client creates a local cache for the identity data. When your app reads and writes keys, it communicates with this local cache . This communication guarantees that all changes you make on the device are immediately available on the device, even when you are offline. When the synchronize method is called, changes from the service are pulled to the device, and any local changes are pushed to the service. At this point, the changes are available to other devices to synchronize.

Initializing the Amazon Cognito Sync client

To initialize the Amazon Cognito Sync client, you must first create a credentials provider. The credentials provider acquires temporary AWS credentials to make it possible for your app to access your AWS resources. You also must import the necessary header files. Use the following steps to initialize the Amazon Cognito Sync client.

Android

Create a credentials provider, following the instructions in Getting credentials.
Import the Amazon Cognito package as follows: import com.amazonaws.mobileconnectors.cognito.*;
Initialize Amazon Cognito Sync. Pass in the Android app context, the identity pool ID, an AWS Region, and an initialized Amazon Cognito credentials provider as follows:
```
CognitoSyncManager client = new CognitoSyncManager(
    getApplicationContext(),
    Regions.YOUR_REGION,
    credentialsProvider);
```

iOS - Objective-C

Create a credentials provider, following the instructions in Getting credentials.

Import AWSCore and Cognito, and initialize AWSCognito as follows:


#import <AWSiOSSDKv2/AWSCore.h>
#import <AWSCognitoSync/Cognito.h>

AWSCognito *syncClient = [AWSCognito defaultCognito];

If you're using CocoaPods, replace <AWSiOSSDKv2/AWSCore.h> with AWSCore.h. Follow the same syntax for the Amazon Cognito import.

iOS - Swift

Create a credentials provider, following the instructions in Getting credentials.

Import and initialize AWSCognito as follows:


import AWSCognito
let syncClient = AWSCognito.default()!

JavaScript

Download the Amazon Cognito Sync Manager for JavaScript.
Include the Sync Manager library in your project.
Create a credentials provider, following the instructions in Getting credentials.

Initialize the Sync Manager as follows:


var syncManager = new AWS.CognitoSyncManager();

Unity

Create an instance of CognitoAWSCredentials, following the instructions in Getting credentials.

Create an instance of CognitoSyncManager. Pass the CognitoAwsCredentials object and a AmazonCognitoSyncConfig, and include at least the Region set, as follows:


AmazonCognitoSyncConfig clientConfig = new AmazonCognitoSyncConfig { RegionEndpoint = REGION };
CognitoSyncManager syncManager = new CognitoSyncManager(credentials, clientConfig);

Xamarin

Create an instance of CognitoAWSCredentials, following the instructions in Getting credentials.

Create an instance of CognitoSyncManager. Pass the CognitoAwsCredentials object and a AmazonCognitoSyncConfig, and include at least the Region set, as follows:


AmazonCognitoSyncConfig clientConfig = new AmazonCognitoSyncConfig { RegionEndpoint = REGION };
CognitoSyncManager syncManager = new CognitoSyncManager(credentials, clientConfig);

Understanding datasets

Amazon Cognito organizes user profile data into datasets. Each dataset can contain up to 1MB of data in the form of key-value pairs. A dataset is the most granular entity that you can synchronize. Read and write operations performed on a dataset only affect the local store until the synchronize method is invoked. Amazon Cognito identifies a dataset by a unique string. You can create a new dataset or open an existing one as follows.

Android


Dataset dataset = client.openOrCreateDataset("datasetname");

To delete a dataset, first call the method to remove it from local storage, then call the synchronize method to delete the dataset from Amazon Cognito as follows:


dataset.delete();
dataset.synchronize(syncCallback);

iOS - Objective-C


AWSCognitoDataset *dataset = [syncClient openOrCreateDataset:@"myDataSet"];

To delete a dataset, first call the method to remove it from local storage, then call the synchronize method to delete the dataset from Amazon Cognito as follows:


[dataset clear];
[dataset synchronize];

iOS - Swift


let dataset = syncClient.openOrCreateDataset("myDataSet")!

To delete a dataset, first call the method to remove it from local storage, then call the synchronize method as follows: to delete the dataset from Amazon Cognito:


dataset.clear()
dataset.synchronize()

JavaScript


syncManager.openOrCreateDataset('myDatasetName', function(err, dataset) {
   // ...
});

Unity


string myValue = dataset.Get("myKey");
dataset.Put("myKey", "newValue");

To delete a key from a dataset, use Remove as follows:


dataset.Remove("myKey");

Xamarin


Dataset dataset = syncManager.OpenOrCreateDataset("myDatasetName");

To delete a dataset, first call the method to remove it from local storage, then call the synchronize method to delete the dataset from Amazon Cognito as follows:


dataset.Delete();
dataset.SynchronizeAsync();

Reading and writing data in datasets

Amazon Cognito datasets function as dictionaries, with values accessible by key. You can read, add, or modify keys and values of a dataset just as if the dataset were a dictionary, as shown in the following examples.

Note that values you write to a dataset only affect the local cached copy of the data until you call the synchronize method.

Android


String value = dataset.get("myKey");
dataset.put("myKey", "my value");

iOS - Objective-C


[dataset setString:@"my value" forKey:@"myKey"];
NSString *value = [dataset stringForKey:@"myKey"];

iOS - Swift


dataset.setString("my value", forKey:"myKey")
let value = dataset.stringForKey("myKey")

JavaScript


dataset.get('myKey', function(err, value) {
  console.log('myRecord: ' + value);
});

dataset.put('newKey', 'newValue', function(err, record) {
  console.log(record);
});

dataset.remove('oldKey', function(err, record) {
  console.log(success);
});

Unity


string myValue = dataset.Get("myKey");
dataset.Put("myKey", "newValue");

Xamarin


//obtain a value
string myValue = dataset.Get("myKey");

// Create a record in a dataset and synchronize with the server
dataset.OnSyncSuccess += SyncSuccessCallback;
dataset.Put("myKey", "myValue");
dataset.SynchronizeAsync();

void SyncSuccessCallback(object sender, SyncSuccessEventArgs e) {
  // Your handler code here
}

Android

To remove keys from a dataset, use the remove method as follows:


dataset.remove("myKey");

iOS - Objective-C

To delete a key from a dataset, use removeObjectForKey as follows:


[dataset removeObjectForKey:@"myKey"];

iOS - Swift

To delete a key from a dataset, use removeObjectForKey as follows:


dataset.removeObjectForKey("myKey")

Unity

To delete a key from a dataset, use Remove as follows:


dataset.Remove("myKey");

Xamarin

You can use Remove to delete a key from a dataset:


dataset.Remove("myKey");

Synchronizing local data with the sync store

Android

The synchronize method compares local cached data to the data stored in the Amazon Cognito Sync store. Remote changes are pulled from the Amazon Cognito Sync store; conflict resolution is invoked if any conflicts occur; and updated values on the device are pushed to the service. To synchronize a dataset, call its synchronize method:


dataset.synchronize(syncCallback);

The synchronize method receives an implementation of the SyncCallback interface, discussed below.

The synchronizeOnConnectivity() method attempts to synchronize when connectivity is available. If connectivity is immediately available, synchronizeOnConnectivity() behaves like synchronize(). Otherwise it monitors for connectivity changes and performs a sync once connectivity is available. If synchronizeOnConnectivity()is called multiple times, only the last synchronize request is kept, and only the last callback will fire. If either the dataset or the callback is garbage-collected, this method won't perform a sync, and the callback won't fire.