Add/Update Data with Named Tags

To associate Named Tags with any cache item, it is required to provide a list of Named Tags, each having two parameters that are key as a string which is the name of the Tag, and value as any primitive type which is the assigned value to the key. NCache then allows you to associate your objects with these Named Tags. You can add items in the cache with Named Tags and then later retrieve these items from the cache using the previously added Named Tags. When items are already added in the cache with certain Named Tags, NCache provides the user with an option to update Named Tags which are already present in the cache. This allows developers to create a searchable index on cache items at runtime.

Prerequisites

Before using the NCache Client-side APIs, ensure that the following prerequisites are fulfilled:

Add Named Tags

NCache provides a custom class, CacheItem that can be used to add data to the cache. This class encapsulates data as its value property. The CacheItem also lets you set additional specifications associated with an object as a property of the Named Tags class. In the following example, Named Tags are set by assigning them as a property of CacheItem.

try
{
  // Precondition: Cache is already connected

  // In an online-store, VIP members are offered 10% discount
  // A customer with VIP membership has signed in to the website

  string customerKey = "Customer:ALFKI";
  Customer customer = cache.Get<Customer>(customerKey);

  // Get customer from database if not found in cache
  if (customer == null)
  {
      // Get customer from the database
      customer = FetchCustomerFromDB("ALFKI");

      // Create a new CacheItem
      var cacheItem = new CacheItem(customer);

      // Creating a Named Tags Dictionary
      var namedTags = new NamedTagsDictionary();

      // Adding Named Tags to the Dictionary
      // Where keys are the names of the tags as string type and values are of primitive type
      namedTags.Add("VIP_Membership_Discount", 0.10 );

      // Setting the Named Tag property of the cacheItem
      cacheItem.NamedTags = namedTags;

      cache.Add(customerKey, cacheItem);
  }
}
catch (OperationFailedException ex)
{
    // NCache specific exception
    if(ex.ErrorCode == NCacheErrorCodes.KEY_ALREADY_EXISTS)
    {
        // An item with the same key already exists
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures 
        // Operation Timeout
        // Operation performed during state transfer
    }
}
catch (Exception ex)
{
    // Any other generic exception like ArgumentNullException or ArgumentException
}
Note

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

Update Named Tags Data through CacheItem

Updating Named Tags through CacheItem requires the item to be first fetched, its Named Tags to be modified, and then it is reinserted into the cache using the Insert method.

The following example first fetches the CacheItem, creates a list with the newly Named Tags, and then reinserts the CacheItem in the cache along with the modified Named Tag list. Hence, it overwrites the value of existing Named Tags.

Warning

Providing Null Named Tag array will throw an ArgumentNullException.

// Precondition: Cache is already connected

// Store Owner has increased VIP membership discount to 12%

string customerKey = "Customer:ALFKI";
Customer customer = cache.Get<Customer>(customerKey);

// Get the customer from database if not found in the cache
if (customer == null)
{
    customer = FetchCustomerFromDB("ALFKI");
}

// Create a new CacheItem
var cacheItem = new CacheItem(customer);

// Creating a Named Tags Dictionary
var newNamedTags = new NamedTagsDictionary();

// Add Named Tag with the updated discount value to the Dictionary
newNamedTags.Add("VIP_Membership_Discount", 0.12);

// Updates the Named Tags with the new Named Tags
// Overrides the value of the existing Named Tags
cacheItem.NamedTags = newNamedTags;

// Reinserts the updated cacheItem into the cache with the modified Named Tags
cache.Insert(customerKey, cacheItem);

Additional Resources

NCache provides a sample application for Named Tags on GitHub.

See Also

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