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Cum sa definesti un provider custom pentru cache

.NET 4.0 ne-a adus si posibilitatea de a controla output caching. Pana in momentul acesta puteam sa controlam obiectele la care sa se faca cache. Daca de exemplu avem o actiune la care doream sa facem cache, puteam sa folosim atributul OutputCacheAttribute, prin care puteam defini durata la care sa se faca cache si prin ce parametri acest cache sa difere.
[OutputCache(Duration=20, VaryByParam="none")]
public ActionResult GetItems()
{
// Executa ceva.
}
In momentul in care se face un call spre actiunea GetItems, se verifica daca aceasta exista in cache si daca cache-ul este valid( nu a expirat iar parametri trasmisi prin VaryByParam sunt identici). Daca conditiile sunt indeplinite atunci rezultatul se incarca automat din cache si se trimite mai departe, altfel se executa actiunea GetItems, iar rezultatul se salveaza in cache.
In cazul in care dorim sa definim un provider propiu pentru output cache este nevoie sa scriem o clasa ce sa mosteneasca din OutputCacheProvider.
    public abstract class OutputCacheProvider : ProviderBase
{
public abstract object Get(string key);
public abstract object Add(string key, object entry, DateTime utcExpiry);
public abstract void Set(string key, object entry, DateTime utcExpiry);
public abstract void Remove(string key);
}
Prin intermediul metodelor care ne sunt puse la dispozitie, putem sa controlam provider-ul in totalitate.
In web.config este este nevoie sa specificam ce fel de output cache sa se foloseasca:
<caching>
<outputCache defaultProvider="NameOutPutCache">
<providers>
<add name="NameOutPutCache"
type="FullLocationOfOutputCacheImplementation" />
</providers>
</outputCache>
</caching>

Pentru a vedea un exemplu de implementare puteti sa va uitati aici: http://galratner.com/blogs/net/archive/2010/06/06/write-your-own-outputcacheprovider.aspx
Mai jos puteti sa gasiti un exemplu de outputcach provider pentru MongoDb:
 public class MongoDbOutputCacheProvider : OutputCacheProvider, IDisposable
{
readonly Mongo _mongo;
readonly IMongoCollection<CacheItem> _cacheItems;

public MongoDbOutputCacheProvider()
{
// Initializare coneciune la MongoDb
_mongo = new Mongo();
_mongo.Connect();

var store = _mongo.GetDatabase("OutputCacheProviderDB");
_cacheItems = store.GetCollection<CacheItem>();
}

public override object Get(string key)
{
// Se cauta elementul cu cheia dorita.
var cacheItem = _cacheItems.FindOne(new { _id = key });

//Se deserializeaza elementul gasit.
if (cacheItem != null) {
if (cacheItem.Expiration.ToUniversalTime() <= DateTime.UtcNow) {
_cacheItems.Remove(cacheItem);
} else {
return Deserialize(cacheItem.Item);
}
}

return null;
}

public override object Add(string key, object entry, DateTime utcExpiry)
{

if (utcExpiry == DateTime.MaxValue)
{
utcExpiry = DateTime.UtcNow.AddMinutes(5);
}

// Se adauga elementul in baza de date.
_cacheItems.Insert(new CacheItem
{
Id = key,
Item = Serialize(entry),
Expiration = utcExpiry
});

return entry;
}

public override void Set(string key, object entry, DateTime utcExpiry)
{
var item = _cacheItems.FindOne(new { _id = key });

if (item != null)
{
// In cazul in care elementul deja exista se face update la informatii.
item.Item = Serialize(entry);
item.Expiration = utcExpiry;
_cacheItems.Save(item);
}
else
{
// Se insereaza un element nou.
_cacheItems.Insert(new CacheItem
{
Id = key,
Item = Serialize(entry),
Expiration = utcExpiry
});
}
}

public override void Remove(string key)
{
// Se elimina din MongoDb.
_cacheItems.Remove(new { _id = key });
}

private static byte[] Serialize(object entry)
{
var formatter = new BinaryFormatter();
var stream = new MemoryStream();
formatter.Serialize(stream, entry);

return stream.ToArray();
}

private static object Deserialize(byte[] serializedEntry)
{
var formatter = new BinaryFormatter();
var stream = new MemoryStream(serializedEntry);

return formatter.Deserialize(stream);
}

public void Dispose()
{
_mongo.Disconnect();
_mongo.Dispose();
}
}

Implementarea completa se poate gasi aici:
http://archive.msdn.microsoft.com/mag201103OutputCache/Release/ProjectReleases.aspx?ReleaseId=5514

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