Implement Cache Loader and Refresher

Note

This feature is only available in NCache Enterprise Edition.

To use Cache Startup Loader and Refresher, the ICacheLoader interface needs to be implemented first. Then the custom logic of loader and refresher can be configured using NCache Web Manager or NCache PowerShell cmdlet. NCache loads and refreshes data from the configured data source based on the custom logic. On cache startup, NCache calls the Init method of the Cache Startup Loader to initialize it. Successful initialization of the cache startup loader, calls the implemented LoadDatasetOnStartup method to load data into the cache. It then uses the RefreshDataset method to refresh the data loaded in the cache on the determined refresh-interval.

In the following example, the client implements the ICacheLoader interface to configure its custom loader and refresher logic. If you configured two datasets from NCache Web Manager: Products and Suppliers. The following implementation loads Products and Suppliers on cache startup. Additionally, it refreshes these datasets on their specified refresh time.

For more details on the components of Cache Loader, refer to the chapter Components of Cache Startup Loader and Refresher.

Prerequisites

Initialize Cache Startup Loader and Refresher

The following code shows how to implement the Init method of the ICacheLoader interface. This method takes parameters as input and assigns values against them.

public void Init(IDictionary<string, string> parameters, string cacheName)
{
    cache = CacheManager.GetCache(cacheName);
    connectionString = parameters.ContainsKey("ConnectionString") ? parameters["ConnectionString"] : null;
    if (connectionString != null)
    {
        connection = new SqlConnection(connectionString);
    }
}
Note

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

Load Data on Cache Startup

The following implementation of LoadDatasetOnStartup method fetches a Product from data source and adds it to the cache. The LoadDatasetOnStartup returns a user context that holds the information about the data loaded in the cache. This method is called when the cache starts to preload data in cache.

public object LoadDatasetOnStartup(string dataset)
{
    // Create a list of datasets to load at cache startup
    IList<object> datasetToLoad;

    switch (dataset.ToLower())
    {
        // If dataset is products, fetch products from data source to load in cache
        case "products":
            datasetToLoad = FetchProductsFromDataSource();

            // Insert fetched products in the cache
            foreach (var product in datasetToLoad)
            {
                string key = $"ProductID:{product.Id}";
                cache.Insert(key, product);
            }
            break;

        // If dataset is suppliers, fetch suppliers from data source to load in cache
        case "suppliers":
            datasetToLoad = FetchSuppliersFromDataSource();

            // Insert fetched suppliers in the cache
            foreach (var supplier in datasetToLoad)
            {
                string key = $"SupplierID:{supplier.Id}";
                cache.Insert(key, supplier);
            }
            break;

        default:
            // Invalid dataset
    }
    // User context is the time at which datasets were loaded in the cache
    object userContext = DateTime.Now;
    return userContext;
}

Refresh Dataset

The following code implements how to refresh the data that has been loaded in the cache on startup whenever cache refresher is invoked. The RefreshDataset method uses the user context returned by the LoadDatasetOnStartup method to verify which data to refresh.

public object RefreshDataset(string dataset, object userContext)
{
    DateTime? lastRefreshTime;
    switch (dataset.ToLower())
    {
        // If dataset is products, fetch updated products from data source
        case "products":
            lastRefreshTime = userContext as DateTime?;
            IList<Product> productsToRefresh = FetchUpdatedProducts(lastRefreshTime) as IList<Product>;

            // Insert updated products in the cache
            foreach (var product in productsToRefresh)
            {
                string key = $"ProductID:{product.Id}";
                CacheItem cacheItem = new CacheItem(product);
                _cache.Insert(key, cacheItem);
            }
            break;

        // If dataset is supplier, fetch updated suppliers from data source
        case "suppliers":
            lastRefreshTime = userContext as DateTime?;
            IList<Supplier> suppliersToRefresh = FetchUpdatedSuppliers(lastRefreshTime) as IList<Supplier>;

            // Insert updated suppliers in the cache
            foreach (var supplier in suppliersToRefresh)
            {
                string key = $"SupplierID:{supplier.Id}";
                CacheItem cacheItem = new CacheItem(supplier);
                _cache.Insert(key, cacheItem);
            }
            break;

        default:
            // Invalid dataset
    }
    // User context is the time at which datasets were refreshed
    userContext = DateTime.Now;
    return userContext;
}

Get Datasets To Refresh

The GetDatasetsToRefresh method implements the custom logic to refresh a pre-configured dataset at runtime based on RefreshPreference . This method takes user context and assigns RefreshPreference depending upon the specified dataset.

public IDictionary<string, RefreshPreference> GetDatasetsToRefresh(IDictionary<string, object> userContexts)
{
    DateTime? lastRefreshTime;
    bool datasetHasUpdated;

    // Create a dictionary for datasets to refresh with their refresh preference
    IDictionary<string, RefreshPreference> DatasetsToRefresh = new Dictionary<string, RefreshPreference>();

    foreach (var dataset in userContexts.Keys)
    {
        switch (dataset.ToLower())
        {
            // If dataset is products, check if dataset has been updated in data source
            // if yes, then refresh the dataset now
            case "products":
                lastRefreshTime = userContexts[dataset] as DateTime?;
                datasetHasUpdated = HasProductDatasetUpdated(dataset, lastRefreshTime);
                if (datasetHasUpdated)
                {
                    DatasetsToRefresh.Add(dataset, RefreshPreference.RefreshNow);
                }
                break;

            // If dataset is suppliers, check if dataset has been updated in data source
            // if yes, then refresh dataset on next time of day
            case "suppliers":
                lastRefreshTime = userContexts[dataset] as DateTime?;
                datasetHasUpdated = HasSupplierDatasetUpdated(dataset, lastRefreshTime);
                if (datasetHasUpdated)
                {
                    DatasetsToRefresh.Add(dataset, RefreshPreference.RefreshOnNextTimeOfDay);
                }
                break;

            default:
                // Invalid dataset
        }
    }
    // Return the dictionary containing datasets to refresh on polling with their refresh preferences
    return DatasetsToRefresh;
}

Dispose All Resources

In the end, calling the Dispose method ensures that you have closed/deleted all resources to prevent wasteage.

public void Dispose()
{
    // Dispose off all resources like
    connection.Close();
}
Note

Configure Cache Loader/Refresher on NCache by referring to Configure Cache Loader and Refresher in Administrator’s Guide for help.

Additional Resources

NCache provides sample application for Cache Loader & Refresher on GitHub.

See Also

Components of Cache Startup Loader and Refresher
Implementation of Cache Loader and Refresher
Data Source Providers (Backing Source)
Custom Cache Dependencies