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.
