Item Level Event Notifications

Item Level Events can be registered to get notifications for specific key/keys. Besides keys, Item Level Events can also be registered using the CacheItem class. The notifications can be received when update or remove operations are performed on specified keys. Item Level Events can be registered using RegisterCacheNotification by providing the implemented callback, EventType, and EventDataFilter.

Important

The key must exist in cache for the event to be registered. Only the update or remove event types can be registered for Item Level Events.

The relevant details of registering Item Level Events are discussed, as follows.

Prerequisites

To learn about the standard prerequisites required to work with all NCache client side features please refer to the given page on Client Side API Prerequisites.
Make sure to enable event notifications using NCache Manager.
For API details, refer to: ICache, CacheItem, EventType, EventDataFilter, RegisterCacheNotification , UnRegisterCacheNotification, CacheDataNotificationCallback.

Implement Callback for Event Notifications

You can implement a callback for events where EventType is specified according to the user's logic for ItemAdded, ItemUpdated or ItemRemoved events. The example below shows how to register callbacks for event notifications.

public void OnCacheDataModification(string key, CacheEventArg args)
{
    switch (args.EventType)
    {
        case EventType.ItemAdded:
            Console.WriteLine($"Item with Key '{key}' has been added to cache '{args.CacheName}'");
            break;

        case EventType.ItemUpdated:
            Console.WriteLine($"Item with Key '{key}' has been updated in the cache '{args.CacheName}'");

            // Item can be used if EventDataFilter is DataWithMetadata or Metadata
            if (args.Item != null)
            {
                Product updatedProduct = args.Item.GetValue<Product>();
                Console.WriteLine($"Updated Item is a Product having name '{updatedProduct.ProductName}' with ID '{updatedProduct.ProductID}' and price '{updatedProduct.UnitPrice}'");
            }
            break;

        case EventType.ItemRemoved:
            Console.WriteLine($"Key '{key}' has been removed from the cache '{args.CacheName}'");
            break;
      }
}

// Precondition: Events have been enabled

// Create a target method
public void onCacheDataModification(String key, CacheEventArg args) 
{
  switch (args.getEventType()) 
  {
    case ItemAdded:
      // Key has been added to the cache
      break;
      case ItemUpdated:
      // 'key' has been updated in the cache
      // get the updated product

      if (args.getItem() != null) 
      {
        Product updateProduct = args.getItem().getValue(Product.class);
        // perform operations
      }
      break;
      case ItemRemoved:
      // 'key' has been removed from the cache
      break;
  }
}

class ItemLevelDataModificationListener extends CacheDataModificationListener
{
  override def onCacheDataModified(key: String, eventArgs: CacheEventArg): Unit = 
  {
    eventArgs.getEventType match 
    {
      case EventType.ItemAdded =>
      // Key has been added to the cache

      case EventType.ItemUpdated =>
        // 'key' has been updated in the cache
        // get the updated product
        if (eventArgs.getItem != null) 
        {
          val updateProduct = eventArgs.getItem.getValue(classOf[Product])
          // perform operations
        }

      case EventType.ItemRemoved =>
      // 'key' has been removed from the cache

    }
  }

  override def onCacheCleared(cacheName: String): Unit = 
  {
    print("Cache cleared.")
  }
}

// Precondition: Events have been enabled

// Create a target method
onCacheDataModified(key, arg) 
{
  if (null != arg.getEventType())
  {
    switch (arg.getEventType())
    {
      // perform operations
      case ncache.EventType.ItemUpdated:
        // key has been updated in cache

        if (args.getItem() != null) 
        {
          Product updateProduct = args.getItem().getValue();
          // perform operations
        }
      break;
      case ncache.EventType.ItemRemoved:
        // key has been removed from cache
      break;
      default:
      break;
    }
  }
}

def on_cache_data_modified(key: str, arg: ncache.CacheEventArg):
    if arg.get_event_type() is not None:
        if arg.get_event_type() is ncache.EventType.ITEM_ADDED:
            # Key has been added to cache
            print("Item added")
        elif arg.get_event_type() is ncache.EventType.ITEM_UPDATED:
            # Key has been updated in cache
            print("Item updated")
        elif arg.get_event_type() is ncache.EventType.ITEM_REMOVED:
            # key has been removed from cache
            print("Item removed")

Note

To ensure the operation is fail-safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Register Item Notifications

Given that callback has been implemented, a target method is created which contains multiple callbacks. The appropriate EventType is provided for monitoring only the specific client operations. These event types include ItemUpdated and ItemRemoved that must be specified by a separate method call. EventDataFilter is specified to quantify the amount of information returned upon an event execution.

Note

If EventDataFilter is not specified, EventDataFilter.None is set automatically.

Here, we explain that how you can register item notifications for a particular item or set of items.

Register Item Notifications for a Particular Item

In order to register item notification for a single item, use the RegisterCacheNotifications method by providing a single key, the EventType and the EventDataFilter. The following example shows how to register item notifications with the ItemUpdated event type for a particular item.

// Key of the cache item to be monitored events
string key = "Product:Chai";

// create CacheDataNotificationCallback object
var dataNotificationCallback = new CacheDataNotificationCallback(OnCacheDataUpdation);

// Register notifications for a specific item being updated in cache 
// EventDataFilter as DataWithMetadata which returns keys along with their entire data
cache.MessagingService.RegisterCacheNotification(key, dataNotificationCallback, EventType.ItemUpdated, EventDataFilter.DataWithMetadata);

// Callback to Update Event Notifications
public void OnCacheDataUpdation(string key, CacheEventArg args)
{
    Console.WriteLine($"Item with Key '{key}' has been updated in the cache '{args.CacheName}'");

    // Item can be used if EventDataFilter is DataWithMetadata or Metadata
    if (args.Item != null)
    {
        Product updatedProduct = args.Item.GetValue<Product>();
        Console.WriteLine($"Updated Item is a Product having name '{updatedProduct.ProductName}' with ID '{updatedProduct.ProductID}' and price '{updatedProduct.UnitPrice}'");
    }
}

try {
  // Precondition: Cache is already connected

  var dataModificationListener = onCacheDataModification(key, args);
  CacheDataModification dataModification = new CacheDataModification(dataModificationListener);

  // Register item notification with "ItemUpdated" event type
  // EventDataFilter as DataWithMetadata which returns keys along with their entire data
  EnumSet<com.alachisoft.ncache.runtime.events.EventType> enumSet = EnumSet.of(EventType.ItemAdded);
  cache.getMessagingService().addCacheNotificationListener(key, dataModification, enumSet, EventDataFilter.DataWithMetadata);

  // Perform your business logic
} catch (OperationFailedException exception) {
  // Exception can occur due to:
  // Connection failures
  // Operation timeout
} catch (Exception exception) {
  // Any generic exception like IllegalArgumentException or NullPointerException
}

try {
    // Precondition: Cache is already connected

    val key = "Product:1001"

    // Register target listener
    val dataModificationListener = ItemLevelDataModificationListener()

    // Register item notification with "ItemUpdated" event type
    // EventDataFilter as DataWithMetadata which returns keys along with their entire data
    val enumSet = List(EventType.ItemUpdated)
    cache.getMessagingService.addCacheNotificationListener(key, dataModificationListener, enumSet, EventDataFilter.DataWithMetadata)

    // Perform your business logic
}
catch {
    case exception: Exception => {
      // Handle any errors
    }
}

try {
  // Precondition: Cache is already initialized

  let dataModificationListener = new ncache.CacheDataModificationListener(
    this.onCacheDataModified,
    this.onCacheCleared
  );
  let key = "Product:1001";

  // Register item notifications with 'ItemUpdated' event type
  // EventDataFilter as DataWithMetadata which returns keys along with their entire data
  let messagingService = await this.cache.getMessagingService();
  await messagingService.addCacheNotificationListener(
    key,
    dataModificationListener,
    ncache.EventType.ItemUpdated,
    ncache.EventDataFilter.DataWithMetadata
  );
} catch (error) {
  // Handle any errors
}

try:
    # Pre-conditions: Cache is already connected &

    key = "Product:1001"

    # Register item notifications with 'ITEM_UPDATED' event type
    # EventDataFilter as DATA_WITH_META_DATA which returns keys along with their
    # entire data
    messaging_service = cache.get_messaging_service()
    messaging_service.add_cache_notification_listener(
        event_listener,
        [ncache.EventType.ITEM_UPDATED],
        ncache.EventDataFilter.DATA_WITH_META_DATA,
        key
    )

except Exception as exp:
    # Handle errors

Register Item Notifications for a Set of Items

In order to register item notifications for a set of items, use the RegisterCacheNotifications method by providing an array of keys, the EventType and the EventDataFilter. The following example shows how to register item notifications with the ItemUpdated event type for a set of item.

// Aarray of keys for items that need to be monitored on events
String[] keys = new String[]
{
    "Product:Chai", "Product:Coffee", "Product:Juice", "Product:Coke"
};

// create CacheDataNotificationCallback object
var dataNotificationCallback = new CacheDataNotificationCallback(OnCacheDataUpdation);

// Register notifications for specific set of items being updated in cache 
// EventDataFilter as DataWithMetadata which returns keys along with their entire data
cache.MessagingService.RegisterCacheNotification(keys, dataNotificationCallback, EventType.ItemUpdated, EventDataFilter.DataWithMetadata);

var dataModificationListener = onCacheDataModification(key, args);
CacheDataModification dataModification = new CacheDataModification(dataModificationListener);

// Fetch all products from database
Product[] products = fetchProductsFromDB();

// Create a new array of keys for which the cache fires notifications
String[] keys = new String[products.length];
int index = 0;
for (var product : products) {
  // Generate a unique cache key for this product
  keys[index] = "Product:" + product.productID;
  index++;
}
// Create EnumSet with ItemUpdated and ItemRemoved event type
EnumSet<EventType> enumSet = EnumSet.of(EventType.ItemUpdated, EventType.ItemRemoved);

// Register item notification with ItemUpdated and ItemRemoved event type
// EventDataFilter as DataWithMetadata which returns keys along with their entire data
var data = cache.getMessagingService().addCacheNotificationListener(key, dataModification, enumSet, EventDataFilter.DataWithMetadata);

// Perform your business logic

// Register target method
val dataModificationListener = ItemLevelDataModificationListener()

// Fetch all products from database
val products = fetchProductsFromDB

// Create a new array of keys for which the cache fires notifications
var keys: List[String] = List()
for (product <- products) 
{ 
  // Generate a unique cache key for this product
  keys = ("Product:" + product.getProductId) :: keys
}

// Create EnumSet with ItemUpdated and ItemRemoved event type
val eventTypes = List(EventType.ItemUpdated, EventType.ItemRemoved)

// Register item notification with ItemUpdated and ItemRemoved event type
// EventDataFilter as DataWithMetadata which returns keys along with their entire data
cache.getMessagingService.addCacheNotificationListener(keys, dataModificationListener, eventTypes, EventDataFilter.DataWithMetadata)

// Perform your business logic

let dataModificationListener = new ncache.CacheDataModificationListener(
  this.onCacheDataModified,
  this.onCacheCleared
);

// Fetch all products from database
let products = this.fetchProductsFromDB();

// Create a new array keys with the specified keys for which the cache fires notifications
let keys = new String[products.length]();
var index = 0;
products.forEach((element) => {
  keys[index] = "Product:1001";
  index++;
});
// Register item notifications with 'ItemUpdated' and 'ItemRemoved' event type
// EventDataFilter as DataWithMetadata which returns keys along with their entire data
let messagingService = await this.cache.getMessagingService();
await messagingService.addCacheNotificationListener(
  keys,
  dataModificationListener,
  ncache.EventType.ItemUpdated,
  ncache.EventDataFilter.DataWithMetadata
);

# Register target method
data_modification_listener = event_listener
# Fetch all products from database
products = fetch_products_from_db()

# Create a array keys with the specified keys for which the cache
# fires notifications
keys = []

for product in products:
    keys.append("Product:" + str(product.get_product_id()))

# Register item notifications with 'ITEM_UPDATED' and 'ITEM_REMOVED' event type
# EventDataFilter as DATA_WITH_META_DATA which returns keys along with their
# entire data
messaging_service = cache.get_messaging_service()
messaging_service.add_cache_notification_listener(
    data_modification_listener,
    [ncache.EventType.ITEM_UPDATED],
    ncache.EventDataFilter.DATA_WITH_META_DATA,
    keys

Register Item Notifications Using CacheItem

CacheItem is a custom class provided by NCache which can be used to add data to the cache. Item Level Events can also be registered with a particular key by using the CacheItem.SetCacheDataNotification method. This method allows you to provide the appropriate information for registering the notifications for the CacheItem.

The example below registers ItemUpdated and ItemRemoved events for a CacheItem.

string key = "Product:Chai";

// Fetch item from cache
CacheItem cacheItem = cache.GetCacheItem(key);

if(cacheItem == null)
{
    Product product = FetchProductFromDB("Chai");
    cacheItem = new CacheItem(product);
}

// create CacheDataNotificationCallback object
var dataNotificationCallback = new CacheDataNotificationCallback(OnCacheDataModification);

// Register events with CaceItem with Item Removed and ItemUpdated EventType
// Set the EventDataFilter as DataWithMetadata which returns keys along with their entire data
cacheItem.SetCacheDataNotification(dataNotificationCallback, EventType.ItemRemoved | EventType.ItemUpdated, EventDataFilter.DataWithMetadata);

//Re-inserts the cacheItem into cache with events registered
cache.Insert(key, cacheItem);

var dataModificationListener = onCacheDataModification(key, args);
CacheDataModification dataModification = new CacheDataModification(dataModificationListener);

// Get product from database
Product product = fetchProductFromDB(productid);

// Create a unique cache key for this product
String productKey = "Product:" + product.productID;

// Create a new CacheItem
CacheItem cacheItem = new CacheItem(product);

// Create EnumSet of ItemUpdated and ItemRemoved event types
EnumSet<EventType> enumSet = EnumSet.of(EventType.ItemUpdated, EventType.ItemRemoved);

// Register events with CacheItem with Item Removed and ItemUpdated EventType
// Set the EventDataFilter as DataWithMetadata which returns keys along with their entire data
cacheItem.addCacheDataNotificationListener(dataModification, enumSet, EventDataFilter.DataWithMetadata);

// Insert the cache item in the cache with events registered
cache.insert(productKey, cacheItem);

// Register target method
val dataModificationListener = ItemLevelDataModificationListener()

// Get product from database
val product = fetchProductFromDB("1001")

// Create a unique cache key for this product
val productKey = "Product:" + product.getProductId

// Create a new CacheItem
val cacheItem = new CacheItem(product)

// Create EnumSet of ItemUpdated and ItemRemoved event types
val eventTypes = List(EventType.ItemUpdated, EventType.ItemRemoved)

// Register events with CacheItem with Item Removed and ItemUpdated EventType
// Set the EventDataFilter as DataWithMetadata which returns keys along with their entire data
cacheItem.addCacheDataNotificationListener(dataModificationListener, eventTypes, EventDataFilter.DataWithMetadata)

// Insert the cache item in the cache with events registered
cache.insert(productKey, cacheItem)

let eventListener = new ncache.CacheDataModificationListener(
  this.onCacheDataModified,
  this.onCacheCleared
);
let messagingService = await this.cache.getMessagingService();
await messagingService.addCacheNotificationListener(
  "key",
  eventListener,
  ncache.EventType.ItemAdded,
  ncache.EventDataFilter.Metadata
);

// Get Product from database against given ProductID
let products = this.fetchProductsFromDB();

// Create a unique cache key for this customer.
let key = "Product:1001";

// Register events with CaceItem with Item Removed and ItemUpdated EventType
// Set the EventDataFilter as DataWithMetadata which returns keys along with their entire data
let messagingService2 = await this.cache.getMessagingService();
await messagingService2.addCacheNotificationListener(
  eventListener,
  ncache.EventType.ItemAdded,
  ncache.EventType.ItemRemoved,
  ncache.EventType.ItemUpdated,
  ncache.EventDataFilter.Metadata
);
let cacheItem = ncache.CacheItem;

//Inserts the cacheItem into cache with events registered
this.cache.insert(key, cacheItem);

# Get Product from database
product = fetch_product_from_db()

# Create a unique cache key for this product.
key = "Product:1001"

# Register events with CacheItem with ITEM_REMOVED and ITEM_UPDATED EventType
# Set the EventDataFilter as DATA_WITH_META_DATA which returns keys along with their entire data
cache_item = ncache.CacheItem(product)
cache_item.add_cache_data_notification_listener(
    event_listener,
    [ncache.EventType.ITEM_REMOVED, ncache.EventType.ITEM_UPDATED],
    ncache.EventDataFilter.DATA_WITH_META_DATA
)

# Inserts the cacheItem into cache with events registered
cache.insert(key, cache_item)

Unregister Item Level Notifications

You can also unregister a previously registered item level notification using the UnRegisterCacheNotification method if you don't want to receive further notifications. For Java, use the removeCacheDataModificationListener method to unregister the registered notifications. Using this method, the appropriate key, callback CacheDataNotificationCallback and EventType must be specified.

The following example shows how to unregister notifications for a specific key.

// Key of cached item to un-register events
string key = "Product:Chai";

// callback method triggered on cache item events 
var dataNotificationCallback = new CacheDataNotificationCallback(OnCacheDataUpdation);

// Unregister notifications for the ItemUpdated EventType for particular key and specify the callback
cache.MessagingService.UnRegisterCacheNotification(key, dataNotificationCallback, EventType.ItemUpdated);

// Unregister notifications for the ItemRemoved EventType for particular key and specify callback
var dataModificationListener = onCacheDataModification(key, args);
EnumSet<EventType> enumSet = EnumSet.of(EventType.ItemRemoved);
cache.getMessagingService().removeCacheNotificationListener(key, dataModificationListener, enumSet);

  // Unregister notifications for the ItemRemoved EventType for particular key

  // Specify callback
  val dataModificationListener = ItemLevelDataModificationListener()
  val enumSet = List(EventType.ItemRemoved)
  cache.getMessagingService.removeCacheNotificationListener("Product1001", dataModificationListener, enumSet)

let eventListener;

// Unregister notifications for the ItemRemoved EventType for the
// particular key and specify the callback
await this.cache.removeCacheNotificationListener(
  "key",
  eventListener,
  ncache.EventType.ItemRemoved
);

# Unregister notifications for the ITEM_REMOVED EventType for the
# particular key and specify the callback
cache.get_messaging_service().remove_cache_notification_listener
    keys="key",
    callablefunction=event_listener,
    eventtypes=[ncache.EventType.ITEM_REMOVED]

Additional Resources

NCache provides a sample application for Item Level Event Notifications on GitHub.

Item Level Event Notifications

Important

Prerequisites

Implement Callback for Event Notifications

Note

Register Item Notifications

Note

Register Item Notifications for a Particular Item

Register Item Notifications for a Set of Items

Register Item Notifications Using CacheItem

Unregister Item Level Notifications

Additional Resources

See Also