Bulk Extensible Database Dependency Usage and Implementation

In Extensible Dependency, each dependency takes time to determine change which might cause an expiration lag. With the increase in the number of custom dependencies, expiration on each item takes time because of which some items remain in the cache way past their expiry.

Note

This feature is only available in the NCache Enterprise for .NET Servers.

To counter this issue, NCache provides another class called BulkExtensibleDependency, where a bulk of custom dependencies and database dependencies are evaluated at the same time. This helps boost the application's performance as the items that have expired are removed from the cache in time. BulkExtensibleDependency is provided at runtime through which the user can evaluate data and database dependency in bulk and call Expire on the dependencies that need to be removed from the cache.

Important

In case your business requirement is a method where an item needs to be individually evaluated instead of in a bulk, then use ExtensibleDependency. Otherwise, you will face performance issues.

Tip

Refer to Custom Cache Dependencies to get acquainted with all cache dependency custom methods provided by NCache.

Prerequisites to Configure Bulk Extensible Database Dependency

Step 1: Implement BulkExtensibleDependency Class

The first step in introducing your own logic for Bulk Extensible Database Dependency is to inherit the BulkExtensibleDependency class.

The following class implements your custom logic to remove multiple items at a time using Bulk Extensible Dependency.

[Serializable]
public class BulkDependency : BulkExtensibleDependency
{
    // Class parameters

    public BulkDependency(string connString, int ProductId)
    {
        connection = DriverManager.GetConnection(connString);
        connection.open();
        productID = ProductId;
    }

    private Dictionary<int,int> UnitsInStockStatus(List<int> productIds)
        {
            String queryString = "your_query_here";
            Dictionary<int, int> productsInfo = new Dictionary<int, int>();

            using (var cmd = new SqlCommand(queryString, connection))
            {
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        int units = 0;
                        Int32.TryParse(reader["UnitsInStock"].ToString(), out units);
                        productsInfo.Add((int)reader.GetValue(0), units);
                    }
                }
            }
            return productsInfo;
        }
    }

    public override void EvaluateBulk(IEnumerable<BulkExtensibleDependency> dependencies)
    {
        List<BulkDependency> dependencyList = new List<BulkDependency>();
        foreach (BulkDependency bulkDependency in dependencies)
        {
            dependencyList.Add(bulkDependency);
        }

        List<int> productIds = GetOutofStockProducts(dependencyList);
        var productsInfo = UnitsInStockStatus(productIds);

        foreach (BulkDependency bulkDependency in dependencyList)
        {
            if (productsInfo.ContainsKey(bulkDependency.productId))
            {
                if (productsInfo[bulkDependency.productId] != bulkDependency.unitsInStock)
                {
                    bulkDependency.Expire();
                }
            }
        }
    }

    private List<int> GetOutofStockProducts()
    {
        List<int> productIds = new List<int>();

        foreach(BulkDependency bulkDependency in dependencies)
            {
                productIds.Add(bulkDependency.productId);
            }
        }
        return productIds;
    }

    private Dispose()
    {
        // Dispose off all resources
    }
    // This class is to be deployed on NCache
}
Important

Do not use this.Expire() to expire an object that isn't valid anymore. Instead, call the .Expire() method on the instance of dependency that needs to be expired, e.g. myDep.Expire()

Step 2: Implement BulkCustomDependencyProvider

To implement a Bulk Extensible Database Dependency provider in your application, use the following code snippet.

A Custom Dependency Provider for Bulk Extensible Dependency implements the logic that you created in Step 1 on the server side. Here's how you can implement your own provider:

public class BulkCustomDependencyProvider : ICustomDependencyProvider
{
    public void Init(IDictionary<string, string> parameters, string cacheName)
    {
        // Initialize cache and class parameters
    }

    public BulkDependency CreateDependency(string key, IDictionary<string, string> dependencyParameters)
    {
        int productId = 0;
        int units = 0;
        string connectionString = "";

        if (dependencyParameters != null)
        {
            if (dependencyParameters.ContainsKey("ProductID"))
                productId = Int32.Parse(dependencyParameters["ProductID"]);

            if (dependencyParameters.ContainsKey("UnitsAvailable"))
                units = Int32.Parse(dependencyParameters["UnitsAvailable"]);

            if (dependencyParameters.ContainsKey("ConnectionString"))
                connectionString = dependencyParameters["ConnectionString"];

            // Create bulk extensible dependency
            BulkDependency dependency = new BulkDependency(connectionString, productId, units);
            return dependency;
        }
    }
    public void Dispose ()
    {
        // Dispose off all resources
    }
}

Step 3: Deploy Implementation on Cache

Deploy this class and all other dependent assemblies on NCache by referring to Deploy Providers in the Administrator's Guide for help.

Step 4: Use Bulk Extensible Dependency

Once the Bulk Extensible Dependency class has been implemented and deployed, it is ready to be used in your application.

The following code shows how to add data into the cache using the Insert() with Bulk Dependency.

// Specify the connection string
string connectionString = ConfigurationManager.AppSettings["connectionstring"];

// Fetch the product to be added to the cache
Product product = FetchProductFromDB(productId);

// Specify the unique key of the item
string key = $"Product:{product.ProductID}";

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

// Create dictionary for dependency parameters
IDictionary<string, string> param = new Dictionary<string, string>();
param.Add("ProductID", products.Id.ToString());
param.Add("ConnectionString", _connectionString);

// Create Bulk Extensible Dependency using Provider and Add it to Cache Item
CustomDependency customDependency = new CustomDependency(ConfigurationManager.AppSettings["ProviderName"], param);
cacheItem.Dependency = customDependency;

// Add cacheItem to the cache with bulk dependency
cache.Insert(key, cacheItem);

Additional Resources

NCache provides a sample application for Bulk Extensible Dependency on GitHub.

See Also

.NET: Alachisoft.NCache.Runtime.Dependencies namespace.