This post adds SQL
Cache Dependency support to the loosely coupled .NET
Cache Provider that I described in the previous post (http://geekswithblogs.net/Rhames/archive/2012/09/11/loosely-coupled-.net-cache-provider-using-dependency-injection.aspx). The sample code is available on github at https://github.com/RobinHames/CacheProvider.git. Each time we want to apply a
cache dependency to a call to fetch or
cache a data item we need to supply an instance of the relevant dependency implementation. This suggests an Abstract Factory will be useful to create
cache dependencies as needed. We can then use Dependency Injection to inject the factory into the relevant consumer. Castle Windsor provides a typed factory facility that will be utilised to implement the
cache dependency abstract factory (see http://docs.castleproject.org/Windsor.Typed-Factory-Facility-interface-based-factories.ashx).
Cache Dependency Interfaces First I created a set of
cache dependency interfaces in the domain layer, which can be used to pass a
cache dependency into the
cache provider. ICacheDependency The ICacheDependency interface is simply an empty interface that is used as a parent for the specific
cache dependency interfaces. This will allow us to place a generic constraint on the
Cache Dependency Factory, and will give us a type that can be passed into the relevant
Cache Provider methods. namespace CacheDiSample.Domain.CacheInterfaces
{
public interface ICacheDependency
{
}
}
ISqlCacheDependency.cs
The ISqlCacheDependency interface provides specific SQL caching details, such as a Sql Command or a database connection and table. It is the concrete implementation of this interface that will be created by the factory in passed into the
Cache Provider.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace CacheDiSample.Domain.CacheInterfaces
{
public interface ISqlCacheDependency : ICacheDependency
{
ISqlCacheDependency Initialise(string databaseConnectionName, string tableName);
ISqlCacheDependency Initialise(System.Data.SqlClient.SqlCommand sqlCommand);
}
}
If we want other types of
cache dependencies, such as by key or file, interfaces may be created to support these (the sample code includes an IKeyCacheDependency interface).
Modifying ICacheProvider to accept
Cache Dependencies
Next I modified the exisitng ICacheProvider<T> interface so that
cache dependencies may be passed into a Fetch method call. I did this by adding two overloads to the existing Fetch methods, which take an IEnumerable<ICacheDependency> parameter (the IEnumerable allows more than one
cache dependency to be included). I also added a method to create
cache dependencies. This means that the implementation of the
Cache Provider will require a dependency on the
Cache Dependency Factory. It is pretty much down to personal choice as to whether this approach is taken, or whether the
Cache Dependency Factory is injected directly into the repository or other consumer of
Cache Provider. I think, because the
cache dependency cannot be used without the
Cache Provider, placing the dependency on the factory into the
Cache Provider implementation is cleaner.
ICacheProvider.cs
using System;
using System.Collections.Generic;
namespace CacheDiSample.Domain.CacheInterfaces
{
public interface ICacheProvider<T>
{
T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry);
T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry,
IEnumerable<ICacheDependency> cacheDependencies);
IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry);
IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData,
DateTime? absoluteExpiry, TimeSpan? relativeExpiry,
IEnumerable<ICacheDependency> cacheDependencies);
U CreateCacheDependency<U>()
where U : ICacheDependency;
}
}
Cache Dependency Factory
Next I created the interface for the
Cache Dependency Factory in the domain layer.
ICacheDependencyFactory.cs
namespace CacheDiSample.Domain.CacheInterfaces
{
public interface ICacheDependencyFactory
{
T Create<T>()
where T : ICacheDependency;
void Release<T>(T cacheDependency)
where T : ICacheDependency;
}
}
I used the ICacheDependency parent interface as a generic constraint on the create and release methods in the factory interface.
Now the interfaces are in place, I moved on to the concrete implementations.
ISqlCacheDependency Concrete Implementation
The concrete implementation of ISqlCacheDependency will need to provide an instance of System.Web.Caching.SqlCacheDependency to the
Cache Provider implementation. Unfortunately this class is sealed, so I cannot simply inherit from this. Instead, I created an interface called IAspNetCacheDependency that will provide a Create method to create an instance of the relevant System.Web.Caching
Cache Dependency type. This interface is specific to the ASP.NET implementation of the
Cache Provider, so it should be defined in the same layer as the concrete implementation of the
Cache Provider (the MVC UI layer in the sample code).
IAspNetCacheDependency.cs
using System.Web.Caching;
namespace CacheDiSample.CacheProviders
{
public interface IAspNetCacheDependency
{
CacheDependency CreateAspNetCacheDependency();
}
}
Next, I created the concrete implementation of the ISqlCacheDependency interface. This class also implements the IAspNetCacheDependency interface. This concrete implementation also is defined in the same layer as the
Cache Provider implementation.
AspNetSqlCacheDependency.cs
using System.Web.Caching;
using CacheDiSample.Domain.CacheInterfaces;
namespace CacheDiSample.CacheProviders
{
public class AspNetSqlCacheDependency : ISqlCacheDependency, IAspNetCacheDependency
{
private string databaseConnectionName;
private string tableName;
private System.Data.SqlClient.SqlCommand sqlCommand;
#region ISqlCacheDependency Members
public ISqlCacheDependency Initialise(string databaseConnectionName, string tableName)
{
this.databaseConnectionName = databaseConnectionName;
this.tableName = tableName;
return this;
}
public ISqlCacheDependency Initialise(System.Data.SqlClient.SqlCommand sqlCommand)
{
this.sqlCommand = sqlCommand;
return this;
}
#endregion
#region IAspNetCacheDependency Members
public System.Web.Caching.CacheDependency CreateAspNetCacheDependency()
{
if (sqlCommand != null)
return new SqlCacheDependency(sqlCommand);
else
return new SqlCacheDependency(databaseConnectionName, tableName);
}
#endregion
}
}
ICacheProvider Concrete Implementation
The ICacheProvider interface is implemented by the CacheProvider class. This implementation is modified to include the changes to the ICacheProvider interface.
First I needed to inject the
Cache Dependency Factory into the
Cache Provider:
private ICacheDependencyFactory cacheDependencyFactory;
public CacheProvider(ICacheDependencyFactory cacheDependencyFactory)
{
if (cacheDependencyFactory == null)
throw new ArgumentNullException("cacheDependencyFactory");
this.cacheDependencyFactory = cacheDependencyFactory;
}
Next I implemented the CreateCacheDependency method, which simply passes on the create request to the factory:
public U CreateCacheDependency<U>() where U : ICacheDependency
{
return this.cacheDependencyFactory.Create<U>();
}
The signature of the FetchAndCache helper method was modified to take an additional IEnumerable<ICacheDependency> parameter:
private U FetchAndCache<U>(string key, Func<U> retrieveData,
DateTime? absoluteExpiry, TimeSpan? relativeExpiry, IEnumerable<ICacheDependency> cacheDependencies)
and the following code added to create the relevant System.Web.Caching.CacheDependency object for any dependencies and pass them to the HttpContext Cache:
CacheDependency aspNetCacheDependencies = null;
if (cacheDependencies != null)
{
if (cacheDependencies.Count() == 1)
// We know that the implementations of ICacheDependency will also implement IAspNetCacheDependency
// so we can use a cast here and call the CreateAspNetCacheDependency() method
aspNetCacheDependencies = ((IAspNetCacheDependency)cacheDependencies.ElementAt(0)).CreateAspNetCacheDependency();
else if (cacheDependencies.Count() > 1)
{
AggregateCacheDependency aggregateCacheDependency = new AggregateCacheDependency();
foreach (ICacheDependency cacheDependency in cacheDependencies)
{
// We know that the implementations of ICacheDependency will also implement IAspNetCacheDependency
// so we can use a cast here and call the CreateAspNetCacheDependency() method
aggregateCacheDependency.Add(((IAspNetCacheDependency)cacheDependency).CreateAspNetCacheDependency());
}
aspNetCacheDependencies = aggregateCacheDependency;
}
}
HttpContext.Current.
Cache.Insert(key, value, aspNetCacheDependencies, absoluteExpiry.Value, relativeExpiry.Value);
The full code listing for the modified CacheProvider class is shown below:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Caching;
using CacheDiSample.Domain.CacheInterfaces;
namespace CacheDiSample.CacheProviders
{
public class CacheProvider<T> : ICacheProvider<T>
{
private ICacheDependencyFactory cacheDependencyFactory;
public CacheProvider(ICacheDependencyFactory cacheDependencyFactory)
{
if (cacheDependencyFactory == null)
throw new ArgumentNullException("cacheDependencyFactory");
this.cacheDependencyFactory = cacheDependencyFactory;
}
public T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry)
{
return FetchAndCache<T>(key, retrieveData, absoluteExpiry, relativeExpiry, null);
}
public T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry,
IEnumerable<ICacheDependency> cacheDependencies)
{
return FetchAndCache<T>(key, retrieveData, absoluteExpiry, relativeExpiry, cacheDependencies);
}
public IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry)
{
return FetchAndCache<IEnumerable<T>>(key, retrieveData, absoluteExpiry, relativeExpiry, null);
}
public IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry,
IEnumerable<ICacheDependency> cacheDependencies)
{
return FetchAndCache<IEnumerable<T>>(key, retrieveData, absoluteExpiry, relativeExpiry, cacheDependencies);
}
public U CreateCacheDependency<U>() where U : ICacheDependency
{
return this.cacheDependencyFactory.Create<U>();
}
#region Helper Methods
private U FetchAndCache<U>(string key, Func<U> retrieveData,
DateTime? absoluteExpiry, TimeSpan? relativeExpiry, IEnumerable<ICacheDependency> cacheDependencies)
{
U value;
if (!TryGetValue<U>(key, out value))
{
value = retrieveData();
if (!absoluteExpiry.HasValue)
absoluteExpiry =
Cache.NoAbsoluteExpiration;
if (!relativeExpiry.HasValue)
relativeExpiry =
Cache.NoSlidingExpiration;
CacheDependency aspNetCacheDependencies = null;
if (cacheDependencies != null)
{
if (cacheDependencies.Count() == 1)
// We know that the implementations of ICacheDependency will also implement IAspNetCacheDependency
// so we can use a cast here and call the CreateAspNetCacheDependency() method
aspNetCacheDependencies =
((IAspNetCacheDependency)cacheDependencies.ElementAt(0)).CreateAspNetCacheDependency();
else if (cacheDependencies.Count() > 1)
{
AggregateCacheDependency aggregateCacheDependency = new AggregateCacheDependency();
foreach (ICacheDependency cacheDependency in cacheDependencies)
{
// We know that the implementations of ICacheDependency will also implement IAspNetCacheDependency
// so we can use a cast here and call the CreateAspNetCacheDependency() method
aggregateCacheDependency.Add(
((IAspNetCacheDependency)cacheDependency).CreateAspNetCacheDependency());
}
aspNetCacheDependencies = aggregateCacheDependency;
}
}
HttpContext.Current.
Cache.Insert(key, value, aspNetCacheDependencies, absoluteExpiry.Value, relativeExpiry.Value);
}
return value;
}
private bool TryGetValue<U>(string key, out U value)
{
object cachedValue = HttpContext.Current.
Cache.Get(key);
if (cachedValue == null)
{
value = default(U);
return false;
}
else
{
try
{
value = (U)cachedValue;
return true;
}
catch
{
value = default(U);
return false;
}
}
}
#endregion
}
}
Wiring up the DI Container
Now the implementations for the
Cache Dependency are in place, I wired them up in the existing Windsor CacheInstaller. First I needed to register the implementation of the ISqlCacheDependency interface:
container.Register(
Component.For<ISqlCacheDependency>()
.ImplementedBy<AspNetSqlCacheDependency>()
.LifestyleTransient());
Next I registered the
Cache Dependency Factory. Notice that I have not implemented the ICacheDependencyFactory interface. Castle Windsor will do this for me by using the Type Factory Facility. I do need to bring the Castle.Facilities.TypedFacility namespace into scope:
using Castle.Facilities.TypedFactory;
Then I registered the factory:
container.AddFacility<TypedFactoryFacility>();
container.Register(
Component.For<ICacheDependencyFactory>()
.AsFactory());
The full code for the CacheInstaller class is:
using Castle.MicroKernel.Registration;
using Castle.MicroKernel.SubSystems.Configuration;
using Castle.Windsor;
using Castle.Facilities.TypedFactory;
using CacheDiSample.Domain.CacheInterfaces;
using CacheDiSample.CacheProviders;
namespace CacheDiSample.WindsorInstallers
{
public class CacheInstaller : IWindsorInstaller
{
public void Install(IWindsorContainer container, IConfigurationStore store)
{
container.Register(
Component.For(typeof(ICacheProvider<>))
.ImplementedBy(typeof(CacheProvider<>))
.LifestyleTransient());
container.Register(
Component.For<ISqlCacheDependency>()
.ImplementedBy<AspNetSqlCacheDependency>()
.LifestyleTransient());
container.AddFacility<TypedFactoryFacility>();
container.Register(
Component.For<ICacheDependencyFactory>()
.AsFactory());
}
}
}
Configuring the ASP.NET SQL
Cache Dependency
There are a couple of configuration steps required to enable SQL
Cache Dependency for the application and database. From the Visual Studio Command Prompt, the following commands should be used to enable the
Cache Polling of the relevant database tables:
aspnet_regsql -S <servername> -E -d <databasename> –ed
aspnet_regsql -S <servername> -E -d CacheSample –et –t <tablename>
(The –t option should be repeated for each table that is to be made available for
cache dependencies).
Finally the SQL
Cache Polling needs to be enabled by adding the following configuration to the <system.web> section of web.config:
<caching>
<sqlCacheDependency pollTime="10000" enabled="true">
<databases>
<add name="BloggingContext" connectionStringName="BloggingContext"/>
</databases>
</sqlCacheDependency>
</caching>
(obviously the name and connection string name should be altered as required).
Using a SQL
Cache Dependency
Now all the coding is complete. To specify a SQL
Cache Dependency, I can modify my BlogRepositoryWithCaching decorator class (see the earlier post) as follows:
public IList<Blog> GetAll()
{
var sqlCacheDependency = cacheProvider.CreateCacheDependency<ISqlCacheDependency>()
.Initialise("BloggingContext", "Blogs");
ICacheDependency[] cacheDependencies = new ICacheDependency[] { sqlCacheDependency };
string key = string.Format("CacheDiSample.DataAccess.GetAll");
return cacheProvider.Fetch(key, () =>
{
return parentBlogRepository.GetAll();
},
null, null, cacheDependencies)
.ToList();
}
This will add a dependency of the “Blogs” table in the database. The data will remain in the
cache until the contents of this table change, then the
cache item will be invalidated, and the next call to the GetAll() repository method will be routed to the parent repository to refresh the data from the database.
