Key Data Dependency Types and Usage [Deprecated]

Key Data Dependency in NCache is a relationship management mechanism that links the lifecycle of dependent cached items to one or more "master" keys. Primarily used to maintain data integrity across related entities - such as ensuring an Order is removed if its associated Product is deleted - this feature automates cache cleanup.

[NOTE] This feature is deprecated, and its use is generally not recommended from version 5.3 SP6 onward.

Note

The dependent item is removed in case of two types of modifications in the master key:

  • Update
  • Remove

Key(s) can have two types of dependencies:

Multilevel Dependency

A cache item can depend on any number of other items in the cache resulting in the formation of a chain. The relationship, in this case, will be a 1:1 relationship. For instance, if there are three data sets in a cache, i.e., Products, Orders, and OrderDetails. An order placed on a particular Product, the key of the OrderDetails depends on the key of the Orders. Similarly, the key of the Orders depends on the key of the Products. This means that if the Products are deleted, the Orders and the OrderDetails are also deleted. The following diagram depicts this scenario visually.

Using Multilevel Key Dependency in NCache

Multiple Dependency

A single item can depend on more than one item in the cache. Similarly, that item may depend on multiple items. This may result in a "1:n" relationship between the items. For example, in a cache, if an Order is placed by a Customer which contains a Product, the Order depends on the Customer and Product. Similarly, the OrderDetails depend on the Orders. The following diagram depicts the whole scenario visually.

Using Multiple Key Dependency in NCache

If the Customer is deleted, Orders and OrderDetails get deleted. Similarly, if the Product is deleted, Orders and OrderDetails get deleted.

Note

You can only specify existing keys in a cache for Key Dependency. A non-existent key specified for Key Dependency will result in an OperationFailedException. Whereas an object can be considered dependent on another key at the time of addition.

Prerequisites

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

Add CacheItem to Cache with Key Dependency

The CacheItem is a custom class provided by NCache that can be used to add data to the cache and lets you set additional metadata associated with an object of this class. This metadata defines the item properties like dependencies, expirations, and more. The Add method adds a new item in the cache, whereas the Insert method adds a new item with dependency. If this CacheItem already exists in the cache, it overwrites its properties.

Important

Note that this API also specifies CacheItem priority for Eviction and Expiration, where the value for that parameter is passed as Default.

The following example adds a CacheItem order to the cache using the Insert method, which is dependent on the customer in the cache, which means as soon as the customer is updated or deleted, the order of the customer is already deleted from the cache.

try
{
      // Precondition: Cache is already connected
      // Get customer from database
      Customer customer = FetchCustomerFromDB("ALFKI");

      // Add customer in cache
      cache.Add(customer.CustomerID, customer);

      // Get order from customer
      Order order = new Order
      {
            OrderID = 10248,
            OrderDate = DateTime.Now,
            ShipAddress = "Carrera 22 con Ave. Carlos Soublette #8-35"
      };

      // Save order to database
      bool isOrderSaved = SaveOrderToDB(order);

      // Generate order Id
      string orderKey = $"Order:{order.OrderID}";

      if (isOrderSaved)
      {
            // Generate an instance of Key Dependency
            CacheDependency dependency = new KeyDependency(customer.CustomerID);

            // Create CacheItem to your desired object
            CacheItem cacheItem = new CacheItem(order);

            // Add Key Dependency to order
            cacheItem.Dependency = dependency;

      // Add order in cache
            cache.Add(orderKey, cacheItem);
      }

      // Create order detail for the order
      OrderDetail orderDetail = new OrderDetail
      {
            OrderID = order.OrderID,
            UnitPrice = 200,
            Discount = 25.5F,
            Quantity = 10,
      };

      // Save order detail to database
      bool isOrderDetailSaved = SaveOrderDetailToDB(orderDetail);

      if (isOrderDetailSaved)
      {
            // Generate order detail Id
            string orderDetailId = $"OrderDetail: {orderDetail.OrderID}";

            // Generate an instance of Key Dependency
            CacheDependency dependency = new KeyDependency(orderKey);

            // Create CacheItem with your desired object
            CacheItem cacheItem = new CacheItem(orderDetail);

            // Apply dependency on order
            cacheItem.Dependency = dependency;

            // Insert order detail in cache with dependency
            cache.Add(orderDetailId, cacheItem);
      }
}
catch (OperationFailedException ex)
{
      // NCache specific exception

      if (ex.ErrorCode == NCacheErrorCodes.DEPENDENCY_KEY_NOT_FOUND)
      {
            // The dependent item does not exist in the cache
      }
      else
      {
            // Exception can occur due to:
            // Connection Failures 
            // Operation Timeout
            // Operation performed during state transfer    
      }
}
catch (Exception ex)
{                
      // Any 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.

Add Key Dependency on Multiple Keys

You can also add Key Dependency to an item which is dependent on multiple keys. This way a single item can be dependent on multiple items using the Add or Insert method. The Add method adds a new item in the cache whereas the Insert method adds a new item with dependency, and if the item already exists in the cache it overwrites its properties. The following example demonstrates this.

// Precondition: Cache is already connected
// Get customer from database
Customer customer = FetchCustomerFromDB();

// Get product from database
Product product = FetchProductFromDB();

// Add customer in cache
cache.Add(customer.CustomerID, customer);

// Add product to cache
string productId = $"Product: {product.ProductID}";
cache.Add(productId, product);

// Get order from customer
Order order = new Order
{
      OrderID = 10248,
      OrderDate = DateTime.Now,
      ShipAddress = "Carrera 22 con Ave. Carlos Soublette #8-35"
};

// Save order to database
bool isOrderSaved = SaveOrderToDB(order);

// Generate order Id
string orderKey = $"Order: {order.OrderID}";

if (isOrderSaved)
{
      string[] dependencyKeys = { productId, customer.CustomerID };
      // Generate an instance of Key Dependency
      CacheDependency dependency = new KeyDependency(dependencyKeys);

      // Create CacheItem with your desired object
      CacheItem cacheItem = new CacheItem(order);

      // Add Key Dependency to order
      cacheItem.Dependency = dependency;

      // Insert order into cache with dependencies
      cache.Insert(orderKey, cacheItem);
}

// Create order detail
OrderDetail orderDetail = new OrderDetail
{
      OrderID = order.OrderID,
      UnitPrice = 200,
      Discount = 25.5F,
      Quantity = 10,
};

// Save order's detail to database
bool isOrderDetailSaved = SaveOrderDetailToDB(orderDetail);

if (isOrderDetailSaved)
{
      // Generate order detail Id
      string orderDetailId = $"OrderDetail: {orderDetail.OrderID}";

      // Generate an instance of Key Dependency
      CacheDependency dependency = new KeyDependency(orderKey);

      // Create CacheItem with your desired object
      CacheItem cacheItem = new CacheItem(orderDetail);

      // Add Key Dependency to order
      cacheItem.Dependency = dependency;

      //  Insert order detail into cache with dependencies
      cache.Insert(orderDetailId, cacheItem);
}

Add Key Dependency to Existing Cache Item

NCache lets you add a Key Dependency to an item already present in the cache, without re-inserting it into the cache. This process occurs through the CacheItemAttribute class which has the property of Dependency to be set against CacheItem. The attribute is then set against the existing key of the item, using the UpdateAttributes method of the Cache class.

The following example shows that an order and a customer are already present in the cache without dependency, and dependency is added using UpdateAttributes such that if the customer is updated or removed in the cache, the order is automatically removed.

// Precondition: Cache is already connected
string orderId = "Order:10248";
string ProductId = "Product:8899";

// Create a Key Dependency
CacheDependency dependency = new KeyDependency(ProductId);

// Create a cache item attribute
CacheItemAttributes itemAttribute = new CacheItemAttributes();

// Set dependency to cache item attribute
itemAttribute.Dependency = dependency;

// Update attribute in cache
cache.UpdateAttributes(orderId, itemAttribute);

Additional Resources

NCache provides a sample application for Key Dependency on GitHub.

See also

.NET: Alachisoft.NCache.Runtime.Dependencies namespace.
Java: com.alachisoft.ncache.runtime.dependencies namespace.
Python: ncache.runtime.dependencies class.
Node.js: Key Dependency class.