public ICacheImplementation Select(TimeSpan durationToCacheItemFor,
StorageStyle cacheStorageStyle,
ExpirationType expirationType)
{
Ensure.That(durationToCacheItemFor.IsGreaterThanZero(), "durationToCacheItemFor");
return _selectorDelegate(durationToCacheItemFor,
cacheStorageStyle,
expirationType,
_implementations);
}
/// <summary>
/// This is the method to be supplied to the constructor of
/// the base type as the delegate to use for cache selection.
/// Selects a cache based on the heuristic of duration to
/// store for, followed by the availability of the requested
/// caching functionality. This logic serves as a workable
/// example, rather than a recommended strategy. For example,
/// the fallback case is handled without error or warning.
/// Public rather than protected for testing purposes.
/// </summary>
/// <remarks>
/// NOTE: BA; should we throw an exception if the user requests
/// a storage strategy that cannot be fulfilled due to
/// limitations of the underlying cache?
/// NOTE: BA; Potentially have a flag to indicate strictness of
/// choice of cache - i.e. does the cache really need to
/// support all the desired features, or can we substitute
/// them?
/// "narrow down choice of caches to those that can be used,
/// then choose the enabled one according to priority".
/// </remarks>
/// <param name = "implementations">Ordered by preference of use
/// with highest pref first.</param>
public static ICacheImplementation SelectCacheImplementation(TimeSpan durationToCacheItemFor,
StorageStyle cacheStorageStyle,
ExpirationType cacheExpirationType,
Dictionary<string, ICacheImplementation>
implementations)
{
Ensure.That<FriendlyExceptions.ArgumentOutOfRangeException>(durationToCacheItemFor.IsGreaterThanZero(),
"durationToCacheFor")
.And<FriendlyExceptions.ArgumentNullException>(implementations.IsNotNull(), "implementations")
.And<FriendlyExceptions.ArgumentException>(implementations.Count.Is(2), "implementations")
.And<MissingCacheImplementationArgumentException>(
implementations.ContainsKey(MemcachedImplementationTypeName), "memcached missing")
.And<MissingCacheImplementationArgumentException>(
implementations.ContainsKey(AspDotNetImplementationTypeName), "asp.net data cache missing");
ICacheImplementation cacheToUse = null;
//simply tries to select memcached if an extended caching period is requested
//otherwise attempts to fallback to ASP.NET data cache. This might occur because
//the caching expiration type is not supported by memcached.
if (durationToCacheItemFor >= LongTermBoundary)
{
if (implementations[MemcachedImplementationTypeName].Supports((cacheExpirationType))
&& implementations[MemcachedImplementationTypeName].IsEnabled)
cacheToUse = implementations[MemcachedImplementationTypeName];
if (cacheToUse == null
&& implementations[AspDotNetImplementationTypeName].Supports((cacheExpirationType))
&& implementations[AspDotNetImplementationTypeName].IsEnabled)
cacheToUse = implementations[AspDotNetImplementationTypeName];
Ensure.That(cacheToUse.IsNotNull(), () => { throw new CacheSelectionException(implementations); });
}
else
{
if (implementations[AspDotNetImplementationTypeName].Supports((cacheExpirationType))
&& implementations[AspDotNetImplementationTypeName].IsEnabled)
cacheToUse = implementations[AspDotNetImplementationTypeName];
if (cacheToUse == null
&& implementations[MemcachedImplementationTypeName].Supports((cacheExpirationType))
&& implementations[MemcachedImplementationTypeName].IsEnabled)
cacheToUse = implementations[MemcachedImplementationTypeName];
Ensure.That(cacheToUse.IsNotNull(), () => { throw new CacheSelectionException(implementations); });
}
return cacheToUse;
}
