Absolute Data Expiration in Cache (2024)

NCache allows you to configure Absolute Expiration with your cache items. This will expire the items at the exact date and time specified by the client. Absolute Expiration can be specified on items that are required for a limited time in the cache. For example, a company announces a flash sale for 24 hours on certain products. These items can then be cached with an Absolute Expiration of 24 hours so they are expired from the cache as soon as the sale ends.

Moreover, this DateTime value is converted to UTC time to cater to the case where the cache server and client are in different time zones. So the items will expire at the exact time that has been specified by the user.

Prerequisites

Add/Update Item with Absolute Expiration

You add/update the cache items to set expiration, using the Insert method. The CacheItem is a custom class provided by NCache that can be used to add data to the cache and also lets you set additional metadata associated with an object of this class. This metadata defines the properties of the item like expiration, dependencies, and more.

The following example sets the value of the Expiration property to Absolute Expiration of 5 minutes for a CacheItem. It adds the CacheItem to the cache if the key does not exist - and updates the item if it exists. This CacheItem will then be removed from the cache after 5 minutes.

// Precondition: Cache is already connected// Get product from database against given product IDProduct product = FetchProductFromDB(1001);// Generate a unique cache key for this productstring key = $"Product:{product.ProductID}";// Create a new CacheItem for this productvar cacheItem = new CacheItem(product);// Set Expiration TimeSpanvar expiration = new Expiration(ExpirationType.Absolute, TimeSpan.FromMinutes(5));cacheItem.Expiration = expiration;// Add/Update item with expirationcache.Insert(key, cacheItem);

Add/Update Item with Configured Default Expirations

You can specify Absolute Expiration in the API using the DefaultAbsolute and DefaultAbsoluteLonger values configured in the NCache Management Center or config.ncconf. This provides the flexibility of changing the value externally if needed, without changing the code.

The following code associates the configured Default Expiration (DefaultAbsolute in this case) with an item and adds it to the cache if the key does not exist in the cache, and updates the item with expiration if the key exists. Once the configured time has elapsed, the item is expired.

// Get product from database against given product IDProduct product = FetchProductFromDB(1001);// Generate a unique cache key for this productstring key = $"Product:{product.ProductID}";// Create a cacheItem instance for productvar cacheItem = new CacheItem(product);// Set Expiration typevar expiration = new Expiration(ExpirationType.DefaultAbsolute);cacheItem.Expiration = expiration;// Add/Update item into the cache with default expirationCacheItemVersion version = cache.Insert(key,cacheItem);

Set Absolute Expiration to Existing Item

NCache also provides the flexibility to set Absolute Expiration to an existing cache item without having to reinsert it into the cache. This is done through the CacheItemAttribute class, which has the AbsoluteExpiration property to be set against the cache item. This sets the exact date and time at which the item should be invalidated from the cache.The attribute is then set against the existing key of the item, using the UpdateAttributes method of ICache.

The following example sets the Absolute Expiration for an item that already exists within the cache with no expiration set. This requires no need of re-adding or re-inserting the item into the cache.

// Precondition: Item already exists in cachestring key = "Product:1001";// Create a CacheItemAttribute for absolute expiration and set its value to 5 secondsvar attr = new CacheItemAttributes();attr.AbsoluteExpiration = DateTime.Now.AddSeconds(5);// Set Absolute Expiration of 5 seconds against existing keycache.UpdateAttributes(key, attr);

Additional Resources

NCache provides a sample application for Absolute Expiration on GitHub.

See Also

.NET: Alachisoft.NCache.Runtime.Caching namespace.
Java: com.alachisoft.ncache.runtime.caching namespace.
Node.js: Expiration class.
Python: ncache.runtime.caching class.