Item Level Events

Item Level Data Notifications can be used when you want to be notified about a limited set of data rather than every operation performed on cache.

Applications register callback method for a specific key in cache using API calls and get a notification when that key gets updated or removed from cache.

These Notifications are asynchronously sent to the client so there is no overhead on client’s activities.

To utilize the API, include the following namespace in your application: Alachisoft.NCache.Web.Caching.

Registering Event with a Particular Item

NCache provides a separate classification of events which can be registered with individual keys. To register update or remove event with particular key(s) RegisterCacheNotification method should be used.

Note

The key must exist in cache for the event to be registered. Only update or remove event types can be registered in item level events.

In the following example, the cache will generate a notification when the appropriate operation is performed on the key.

// Create a target method
public static void OnCacheDataModification(string key, CacheEventArg args)
{
    switch (args.EventType)
    {
        case EventType.ItemAdded:
            //perform appropriate operations
            break;
        case EventType.ItemRemoved:
            //perform appropriate operations
            break;
        case EventType.ItemUpdated:
            //perform appropriate operations
            break;
    }
}
//Register target method
CacheDataNotificationCallback dataNotificationCallback = new CacheDataNotificationCallback(OnCacheDataModification);
try
{
    // Register notification with appropriate event type on existing key
    cache.RegisterCacheNotification(key, dataNotificationCallback,
    EventType.ItemRemoved | EventType.ItemUpdated,
    EventDataFilter.DataWithMetadata);

}
catch (Exception ex)
{
    // handle exception
}

Registering Events with CacheItem

An event can also be registered with a particular key by registering as a property of CacheItem. The SetCacheDataNotification method in CacheItem can be used to provide all appropriate information for registering the notification.

// Create a target method
public static void OnCacheDataModification(string key, CacheEventArg args)
{
    switch (args.EventType)
    {
      case EventType.ItemAdded:
      //perform appropriate operations
      break;
      case EventType.ItemRemoved:
      //perform appropriate operations
      break;
      case EventType.ItemUpdated:
      //perform appropriate operations
      break;
    }
}

// Register target method
CacheDataNotificationCallback dataNotificationCallback = new CacheDataNotificationCallback(OnCacheDataModification);
try
{
      Product product = new Product();
      product.ProductID = 1001;
      product.ProductName = "Chai";
      product.UnitsInStock = 15;

      CacheItem cacheItem = new CacheItem(product);

      // Registering event with cacheItem
      cacheItem.SetCacheDataNotification(dataNotificationCallback, EventType.ItemRemoved | EventType.ItemUpdated, EventDataFilter.DataWithMetadata);

      string key = "Product:" + product.ProductID;
      // Register

      cache.Insert(key, cacheItem);
}
catch (Exception ex)
{
      // handle exception
}

Un-registering Item Level Notification

You can also unregister a previously registered item level notification using the UnRegisterCacheNotification method. In this example, the appropriate key, callback CacheDataNotificationCallback and EventType must be specified.

try
{
  cache.UnRegisterCacheNotification(key, callback, EventType);
}
catch (Exception ex)
{
  // handle exception
}