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Configuring Read-Through Provider
The following steps should be followed to configure and implement the Read-Through provider with NCache.
Implementing IReadThruProvider Interface
To implement IReadThruProvider, add following references in the provider assembly.
Alachisoft.NCache.Runtime.dll
Create a class that implements Alachisoft.NCache.Runtime.DatasourceProviders.IReadThruProvider interface and deploy it using NCache Manger. NCache framework will internally use this class to load the data from the configured data source if it is not available in the cache.
IReadThru Interface
Public void Init(System.Collections.IDictionary parameters, StringcacheId);
Public void Dispose();
Public void LoadFromSource(string key, out ProviderCacheItemcacheItem);
Public Dictionary<string, ProviderCacheItem> LoadFromSource(string[] keys);
Sample Code for IReadThruProvider
// Contains methods used to read an object by its key from the master data source.
// Contains methods used to read an object by its key from the master data source.
public class SampleReadThruProvider : IReadThruProvider
{
private SqlConnection _connection;
//Perform tasks like allocating resources or acquiring connections
public void Init(IDictionary parameters, string cacheId)
{
object connStringObject = parameters["connstring"];
string connString = connStringObject == null ? "" : connStringObject.ToString();
if (connString != "")
_connection = new SqlConnection(connString);
try
{
_connection.Open();
}
catch (Exception ex)
{
//handle exception
}
}
//Responsible for loading an item from the external data source.
public void LoadFromSource(string key, out ProviderCacheItem cacheItem)
{
//where LoadFromDataSource is the dummy method to load data from data source.
object value = LoadFromDataSource(key);
cacheItem = new ProviderCacheItem(value);
cacheItem.ResyncItemOnExpiration = true;
}
//Perform tasks associated with freeing, releasing, or resetting resources.
public void Dispose()
{
if (_connection != null)
_connection.Close();
}
//Responsible for loading bulk of items from the external data source.
public Dictionary<string, ProviderCacheItem>LoadFromSource(string[] keys)
{
try
{
Dictionary<string, ProviderCacheItem> dictionary = new Dictionary<string, ProviderCacheItem>();
string key = null;
for (int index = 0; index <keys.Length; index++)
{
key = keys[index];
//where LoadFromDataSource is the dummy method to load data from data source.
dictionary.Add(key, new ProviderCacheItem(LoadFromDataSource(key)));
}
return dictionary;
}
catch (Exception exp)
{
Throw;
}
}
private object LoadFromDataSource(string key)
{
object retrievedObject = null;
// load item from your data source and populate retrieved Object
return retrievedObject;
}
}
After implementing and deploying this provider, direct calls can be made to NCache to get the required items. If item is not locally available in cache store, NCache will use "LoadFromSource" method in specified data access class to load items from data source.
Using Read-Through with Basic Operations
This section will explain the use of read-through provider after configuring and deploying it. NCache supports multiple read-through providers with an applications.
Add the following namespaces in application:
using Alachisoft.NCache.Web.Caching;
using Alachisoft.NCache.Runtime.DatasourceProviders;
using Alachisoft.NCache.Runtime;
NCache provides Alachisoft.NCache.Web.Caching.DSReadOption enum to specify Read thru option in APIs.
Multiple read-through providers can be configured through NCache. Default read-through provider will be called if specific provider name is not mentioned through API. You can also use providers other than default by using provider specific overloads of APIs.
Product product=null;
try
{
string key = "Product:1001";
object data = cache.Get(key, DSReadOption.ReadThru);
if (data != null)
{
product = (Product)data;
}
}
catch (OperationFailedException exp)
{
//handle exception }
For better understanding of the these operations review Bulk Operations. In this scenario, use the following API
try
{
String[] keys = { "Product:1001", "Product:1002", "Product:1003", "Product:1004" };
IDictionary resultSet = cache.GetBulk(keys, DSReadOption.ReadThru);
//IDictionary contains cached keys and values
}
catch (OperationFailedException exp)
{
//handle exception
}
For this scenario, use the following API.
string key = "Product:1001";
Product product=null;
try
{
CacheItem data = cache.GetCacheItem(key, DSReadOption.ReadThru);
if (data!= null)
{
product = (Product)data.Value;
}
}
catch (Exception exp)
{
//handle exception
}
Please note that you can specify default provider through NCManager or through client.ncconf placed in config folder of NCache installation directory. If provider name is not provided in both API and client.ncconf, default provider will automatically be used.
<cache id="mycache" default-readthru-provider="defaultProviderName" client-cache-id="" client-cache-syncmode="optimistic" default-writethru-provider="" load-balance="True" server-runtime-context="NCACHE">
...
</cache>
CacheInitParam can also be used to specify providers.
NCache logs the warnings in Application event log in case of an exception during loading the assemblies.
See Also
Data Source Providers Overview | Read-Through Caching | Write-Through Caching | Configuring Write-Through Provider | Configuring Data Source Providers | Dynamic Compact Serialization | WAN Replication Through Bridge | Custom Dependency | Client Side API Programming
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