Add Data to Cache

After successfully connecting to the cache and gaining a valid cache handle, you can add data to the cache. NCache provides the Add() method and its overloads to facilitate adding objects to cache for the first time.

Prerequisites

Custom Object

You can add an object of a custom class to the cache using various overloads of the Add() method.

Warning

If the key already exists, "The specified key already exists" exception will be thrown.

The following example adds an object of Product class and its associated key into the cache. This returns CacheItemVersion. The code sample then checks whether the key has been successfully added to the cache or not.

Tip

One quick way to verify whether an item has been added is to use either of the following property of the Cache class:

  • Count returns the number of items present in the cache.
  • Contains verifies if a specified key exists in the cache.
Note

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

try
{
    // Pre-condition: 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}";

    // Add Product object to cache
    CacheItemVersion version = cache.Add(key, product);

    // Item added in cache successfully
}
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 generic exception like ArgumentNullException or ArgumentException
}

CacheItem

You can add data with metadata to the cache by encapsulating it in NCache CacheItem class.

Warning

If the key already exists, "The specified key already exists" exception will be thrown.

Tip

One quick way to verify whether an item has been added is to use either of the following properties of the Cache class:

  • Count returns the number of items present in the cache.
  • Contains verifies if a specified key exists in the cache.

The following example adds a basic CacheItem containing the Product object into the cache. Additional properties will be set against the CacheItem in successive chapters.

Note

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

try 
{
    // Pre-condition: 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
    // You can OPTIONALLY specify multiple properties e.g. Priority, Expiration
    // These properties are explained in successive chapters
    var cacheItem = new CacheItem(product);

    // Add CacheItem to cache
    CacheItemVersion version = cache.Add(key, 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 generic exception like ArgumentNullException or ArgumentException
}

CacheItem with Location Affinity

Note

This feature is only available in NCache Enterprise Edition.

You can also add a cache item using NCache Location Affinity syntax. Location Affinity will store the CacheItem created with an identical key at the same node so that when the data is fetched from the cache, the extra matching cost is saved.

Note

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

try 
{
    // Pre-condition: Cache is already connected

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

    // Unique product key for this product
    string productKey = "Product:1001";

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

    // Add CacheItem to cache
    CacheItemVersion version = cache.Add(productKey, productCacheItem);

    // Get order from database against given order ID
    Order order = FetchOrderFromDB(17);

    // Unique order key for this order using Location Affinity syntax
    // This will create an affinity for this orderKey with the respective productKey
    string orderKey = "Order_{Product:1001}";

    var orderCacheItem = new CacheItem(order);

    // Add order with Location Affinity to cache
    CacheItemVersion version = cache.Add(orderKey, orderCacheItem);

}
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 generic exception like ArgumentNullException or ArgumentException
}

JsonObject

Note

This feature is only available in NCache Enterprise Edition.

JsonObject is a class that represents JObject in JSON standards in NCache's domain. You can add attributes to the JsonObject using the AddAttribute method where you have to specify an attribute name and a value as JsonValue or JsonValueBase. Attribute name is case sensitive and cannot be redundant and in case of redundant attributes, exception is thrown.

Note

In order to use JsonValueBase, please add the following namespace in your application:

  • Alachisoft.NCache.Runtime.JSON

The example below creates a JsonObject product along with the attributes and then adds it to the cache. 

try
{
    // Pre-Condition: Cache is already connected
    // Cache is JSON serialized

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

    // Create a unique key for the object
    string key = $"Product:{product.ProductID}";

    // Create a new JSON object and set attributes
    // string values need to be added with JsonValue
    var jsonProduct = new JsonObject();
    jsonProduct.AddAttribute("ProductID", product.ProductID);
    jsonProduct.AddAttribute("ProductName", (JsonValue)product.ProductName);
    jsonProduct.AddAttribute("Category", (JsonValue)product.Category);
    jsonProduct.AddAttribute("UnitPrice", product.UnitPrice);
    jsonProduct.AddAttribute("UnitsInStock", product.UnitsInStock);

    // Create a new CacheItem for product and then insert
    var cacheItem = new CacheItem(jsonProduct);

    // Add object in the cache with the key
    cache.Add(key, cacheItem);

    // JsonObject will successfully be added to the cache
}
catch (OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.ATTRIBUTE_ALREADY_EXISTS)
    {
        // An attribute already exists with the same name
    }
    else if (ex.ErrorCode == NCacheErrorCodes.REFERENCE_TO_SELF)
    {
        // No object can contain a reference to itself
    }
    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
}

JsonArray

JsonArray represents JArray in JSON standards in NCache’s domain mapping arrays or list like collections in NCache’s domain to JArray according to JSON conventions. JsonArray is quite similar to JsonObject, with the difference of JsonObject being a key, value pair whereas JsonArray being a collection.

The values added in JsonArray can either be JsonValue, JsonObject, JsonNull or even another JsonArray; provided it is not adding itself to itself.

The following example creates a JsonArray and adds it to the cache.

try
{
    // Pre-Condition: Cache is already connected
    // Cache is JSON serialized

    // Create a new JsonArray
    var jsonArray = new JsonArray();

    // Get top ten products from the data source
    Product[] products = FetchTop10Products();

    // Convert these products in JsonObjects
    foreach (Product product in products)
    {
        // Create jsonObject and set its attributes
        // ProductName is string so it needs to be added with JsonValue
        var jsonProduct = new JsonObject();
        jsonProduct.AddAttribute("ProductID", product.ProductID);
        jsonProduct.AddAttribute("ProductName", (JsonValue)product.ProductName);
        jsonProduct.AddAttribute("Category", (JsonValue)product.Category);
        jsonProduct.AddAttribute("UnitPrice", product.UnitPrice);
        jsonProduct.AddAttribute("UnitsInStock", product.UnitsInStock);

        // Add jsonObjects to the jsonArray
        jsonArray.Add(jsonProduct);
    }
    // Create a unique key for the array
    string key = "Products";

    // Create a new CacheItem for product and then insert
    var cacheItem = new CacheItem(jsonArray);

    // Add the array in the cache with the key
    cache.Add(key, cacheItem);

}
catch(OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.ATTRIBUTE_ALREADY_EXISTS)
    {
        // An attribute already exists with the same name
    }
    else if (ex.ErrorCode == NCacheErrorCodes.REFERENCE_TO_SELF)
    {
        // No object can contain a reference to itself
    }
    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
}

Bulk Items

AddBulk() adds an array of CacheItem to the cache with the corresponding cache keys. This method returns a dictionary of all the keys that failed to add, along with the failure reason.

Note

For any keys that fail to add, the failure reason will be returned as an IDictionary.

The following code adds a bulk of product items to the cache. If there are any keys that failed to add, the keys can be handled according to your business needs.

Note

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

try
{
    // Pre-condition: Cache is already connected

    // Fetch all products from database
    Product[] products = FetchProductsFromDB();

    //Create dictionary of items to be added to cache
    IDictionary<string, CacheItem> dictionary = new Dictionary<string, CacheItem>();

    foreach (var prod in products)
    {
        string key = $"Product:{prod.ProductID}";
        var cacheItem = new CacheItem(prod);

        //Add dictionary to cache
        dictionary.Add(key, cacheItem);
    }

    // Add bulk data
    IDictionary<string, Exception> keysFailedToAdd = cache.AddBulk(dictionary);

    //Check if keys failed to add
    if (keysFailedToAdd.Count > 0)
    {
        foreach (KeyValuePair<string, Exception> entry in keysFailedToAdd)
        {
            // Check failure reason
            if (entry.Value is OperationFailedException)
            {
                var exception = entry.Value as OperationFailedException;

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

Asynchronous API

Note

This feature is only available in NCache Enterprise Edition.

AddAsync() adds an item to the cache asynchronously and returns an object of the Task class which can be further used according to the business needs of the client application. 

try 
{
    // Pre-condition: 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}";

    // Add Product object to cache
    Task task = cache.AddAsync(key, product);

    //This task object can be used as per your business needs
    if (task.IsFaulted)
    {
        // Task completed due to an unhandled exception
    }
}
catch (OperationFailedException ex)     
{
    // NCache specific exception
    // Exception can occur due to Connection Failure
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Using ICache.Add for Distributed Locking

Due to its versatile nature, another wide use of Add operation is in locking the cache if it is being used by multiple applications.

For example, an environment is set such that as soon as any application connects to the cache, it adds a specific key which is known to all applications. And once the application is done using the cache, it removes the key from the cache. If the key is added successfully, it can proceed to use the cache according to its logic. However, if the key already exists, it means the cache is already being used by an application and is "locked".

This is described in steps in the following diagram:

Add Data to Cache

  1. App A and App B add the "WorkStarted" key as soon as the cache is started.

  2. The key passed by App A is added to the cache before the one passed by App B.

  3. App B gets a "The specified key already exists" exception. In this scenario, App B will wait for App A to finish its work, i.e., until it can successfully add the "WorkStarted" key.

  4. App A removes the key from the cache once done with its work.

  5. App B adds the key to cache again.

  6. The key is added by App B successfully, locking the cache for other applications.

Additional Resources

NCache provides the sample application for Basic Operations on GitHub.

See Also

Data Structures in Cache
JSON Data in cache
Update Existing Data in Cache
Retrieve Existing Cache Data
Remove Data from Cache
How to Connect to Cache