Absolute Data Expiration in Cache

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.

Note

This feature is also available in NCache Community Edition, except for the ability to add/update items with Default Expirations.

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.
For API details, refer to: ICache, CacheItem, CacheItemAttributes, Contains, Count, Expiration, Insert, UpdateAttributes.

Install either of the following NuGet packages in your .NET client application:
- Enterprise: Install-Package Alachisoft.NCache.SDK -Version 4.9.1.0
- Professional: Install-Package Alachisoft.NCache.Professional.SDK -Version 4.9.1.0
Create a new Console Application.
Make sure that the data being added is serializable.
Add NCache References by locating %NCHOME%\NCache\bin\assembly\4.0 and adding Alachisoft.NCache.Web and Alachisoft.NCache.Runtime as appropriate.
Include the Alachisoft.NCache.Web.Caching namespace in your application.
To learn more about the NCache Legacy API, please download the NCache 4.9 documents available as a .zip file on the Alachisoft Website.

Add/Update Item with Absolute Expiration

You can 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.

Tip

You can monitor/verify expiration through:

"Cache Count" Counter in the NCache Monitor or PerfMon Counters.
Using cache.Contains after the expiration interval has elapsed.
Using cache.Count before and after specifying the expiration.

// Precondition: Cache is already connected
// Get product from database against given product ID
Product product = FetchProductFromDB(1001);

// Generate a unique cache key for this product
string key = $"Product:{product.ProductID}";

// Create a new CacheItem for this product
var cacheItem = new CacheItem(product);

// Set Expiration TimeSpan
var expiration = new Expiration(ExpirationType.Absolute, TimeSpan.FromMinutes(5));

cacheItem.Expiration = expiration;

// Add/Update item with expiration
cache.Insert(key, cacheItem);

// Precondition: Cache is already connected
// Get product from database against given product ID
Product product = fetchProductFromDB(1001);

// Generate a unique cache key for this product
String key = "Product:" + product.getProductID();

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

// Set Expiration type and TimeSpan
Expiration expiration = new Expiration(ExpirationType.Absolute, TimeSpan.FromMinutes(5));

cacheItem.setExpiration(expiration);

// Add/Update item in cache with expiration
cache.insert(key, cacheItem);

# Precondition: Cache is already connected
# Get product from database against given product ID
product = fetch_product_from_db()

# Generate a unique cache key for this product
key = "Product:" + product.get_product_id()

# Create a new CacheItem for this product
cache_item = ncache.CacheItem(product)

# Set Expiration type and TimeSpan
expiration = ncache.Expiration(ncache.ExpirationType.ABSOLUTE, ncache.TimeSpan.from_minutes(5))

cache_item.set_expiration(expiration)

# Add/Update item in cache with expiration
cache.insert(key, cache_item)

// This is an async method
// Precondition: Cache is already connected
// Get product from database against given product ID
var product = this.fetchProductFromDB(1001);

// Generate a unique cache key for this product
var key = "Product:" + product.getProductID();

// Create a new CacheItem for this product
// You also need to specify the FQN (Fully Qualified Name) of the class
var cacheItem = new ncache.CacheItem(product,"FQN.Product");

// Set Expiration type and TimeSpan
var expiration = new ncache.Expiration(ncache.ExpirationType.Absolute, ncache.TimeSpan.FromMinutes(5));

cacheItem.setExpiration(expiration);

// Add/Update item in cache with expiration
await this.cache.insert(key, cacheItem);

// Using NCache Enterprise 4.9.1
// Precondition: Cache is already connected
// Get product from database against given product ID
Product product = FetchProductFromDB(1001);

// Generate a unique cache key for this product
string key = $"Product:{product.ProductID}";
CacheItem cacheItem = new CacheItem(product);

// Updating absolute expiration of 5 min through Add API.
cache.Insert(key, product, null, System.DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.Default);

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.

Important

To enable Default Expiration, it is mandatory that you enable it through the NCache Management Center or config.ncconf.

// Precondition: Cache is already connected
// Get product from database against given product ID
Product product = FetchProductFromDB(1001);

// Generate a unique cache key for this product
string key = $"Product:{product.ProductID}";

// Create a cacheItem instance for product
var cacheItem = new CacheItem(product);

// Set Expiration type
var expiration = new Expiration(ExpirationType.DefaultAbsolute);

cacheItem.Expiration = expiration;

// Add/Update item into the cache with default expiration
CacheItemVersion version = cache.Insert(key,cacheItem);

// Precondition: Cache is already connected
// Get product from database against given product ID
Product product = fetchProductFromDB(1001);

// Generate a unique cache key for this product
String key = "Product:" + product.getProductID();

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

// Set Expiration type
Expiration expiration = new Expiration(ExpirationType.DefaultAbsolute);

cacheItem.setExpiration(expiration);

// Add/Update item into the cache with default expiration
CacheItemVersion version = cache.insert(key, cacheItem);

# Precondition: Cache is already connected
# Get product from database
product = fetch_product_from_db()

# Generate a unique cache key for this product
key = "Product:" + product.get_product_id()

# Create a new CacheItem for this product
cache_item = ncache.CacheItem(product)

# Set Expiration type and TimeSpan
expiration = ncache.Expiration(ncache.ExpirationType.DEFAULT_ABSOLUTE)

cache_item.set_expiration(expiration)

# Add/Update item in cache with expiration
version = cache.insert(key, cache_item)

// Precondition: Cache is already connected
// This is an async method
// Get product from database against given product ID
var product = this.fetchProductFromDB(1001);

// Generate a unique cache key for this product
var key = "Product:" + product.getProductID();

// Create a cacheItem instance for product
// You also need to specify the FQN(Fully Qualified Name) of the class
var cacheItem = new ncache.CacheItem(product,"FQN.Product");

// Set Expiration TimeSpan
var expiration = new ncache.Expiration(ncache.ExpirationType.DefaultAbsolute);

cacheItem.setExpiration(expiration);

var version = await this.cache.insert(key, cacheItem);

// Using NCache Enterprise 4.9.1
// Precondition: Cache is already connected

// Get product from database against given product ID
Product product = FetchProductFromDB("1001");

// Generate a unique cache key for this product
string key = $"Product:{product.ProductID}";
CacheItem cacheItem = new CacheItem(product);

// Updating absolute expiration of 5 min through Add API.
cache.Insert(key, product, null, Cache.DefaultAbsolute, Cache.NoSlidingExpiration, CacheItemPriority.Default);

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: Cache is already connected
// Precondition: Item already exists in cache
string key = "Product:1001";

// Create a CacheItemAttribute for absolute expiration and set its value to 5 seconds
var attr = new CacheItemAttributes();
attr.AbsoluteExpiration = DateTime.Now.AddSeconds(5);

// Set Absolute Expiration of 5 seconds against existing key
cache.UpdateAttributes(key, attr);

// This is an async method
// Precondition: Cache is already connected
// Precondition: Item already exists in cache
var key = "Product:1001";

// Create a CacheItemAttribute for absolute expiration and set its value to 5 seconds
var time = new Date().getSeconds()+5;
var attr = new ncache.CacheItemAttributes();

attr.setAbsoluteExpiration(time);

// Set Absolute Expiration of 5 seconds against existing key
await this.cache.updateAttributes(key, attr);

// Precondition: Cache is already connected
// Precondition: Item already exists in cache
String key = "Product:1001";

// Create a CacheItemAttribute for absolute expiration and set its value to 5 seconds
Calendar calendar = Calendar.getInstance();
calendar.add(Calendar.SECOND, 5);

CacheItemAttributes attr = new CacheItemAttributes();

attr.setAbsoluteExpiration(calendar.getTime());

// Set Absolute Expiration of 5 seconds against existing key
cache.updateAttributes(key, attr);

# Precondition: Cache is already connected
# Precondition: Item already exists in cache
key = "Product:1001"

# Create a CacheItemAttribute for absolute expiration and set its value to 5 seconds
time = datetime.now() + timedelta(seconds=5)
attr = ncache.CacheItemAttributes()

attr.set_absolute_expiration(time)

# Set Absolute Expiration of 5 seconds against existing key
cache.update_attributes(key, attr)

// Using NCache Enterprise 4.9.1
// Precondition: Cache is already connected
// Precondition: Item already exists in cache
string key = "1001";

// Get product from database against given product ID
Product product = FetchProductFromDB(key);

//updating AbsoluteLonger expiration with configured value
cache.Insert(key, product, null, Cache.DefaultAbsoluteLonger, Cache.NoSlidingExpiration, CacheItemPriority.Default);

Additional Resources

NCache provides a sample application for Absolute Expiration on GitHub.