/// <summary>
/// Attempt to return an object from the cache. If the item doesn't
/// exist or returns an error, call a Func to return the latest
/// version of an object and insert the result in the cache.
///
/// For most Internet applications, this method is the best method to
/// call to fetch static data (i.e. images) from the network.
/// </summary>
/// <param name="blobCache">The cache to get the item.</param>
/// <param name="key">The key to associate with the object.</param>
/// <param name="fetchFunc">A Func which will asynchronously return
/// the latest value for the object should the cache not contain the
/// key.
///
/// Observable.Start is the most straightforward way (though not the
/// most efficient!) to implement this Func.</param>
/// <param name="absoluteExpiration">An optional expiration date.</param>
/// <typeparam name="T">The type of item to get.</typeparam>
/// <returns>A Future result representing the deserialized object from
/// the cache.</returns>
public static IObservable <T> GetOrFetchObject <T>(this IBlobCache blobCache, string key, Func <IObservable <T> > fetchFunc, DateTimeOffset?absoluteExpiration = null)
{
return(blobCache.GetObject <T>(key).Catch <T, Exception>(_ =>
{
var prefixedKey = blobCache.GetHashCode().ToString(CultureInfo.InvariantCulture) + key;
var result = Observable.Defer(fetchFunc)
.Do(x => blobCache.InsertObject(key, x, absoluteExpiration))
.Finally(() => _inflightFetchRequests.TryRemove(prefixedKey, out var _))
.Multicast(new AsyncSubject <T>()).RefCount();
return (IObservable <T>)_inflightFetchRequests.GetOrAdd(prefixedKey, result);
}));
}
/// <summary>
/// Attempt to return an object from the cache. If the item doesn't
/// exist or returns an error, call a Func to return the latest
/// version of an object and insert the result in the cache.
///
/// For most Internet applications, this method is the best method to
/// call to fetch static data (i.e. images) from the network.
/// </summary>
/// <param name="key">The key to associate with the object.</param>
/// <param name="fetchFunc">A Func which will asynchronously return
/// the latest value for the object should the cache not contain the
/// key.
///
/// Observable.Start is the most straightforward way (though not the
/// most efficient!) to implement this Func.</param>
/// <param name="absoluteExpiration">An optional expiration date.</param>
/// <returns>A Future result representing the deserialized object from
/// the cache.</returns>
public static IObservable <T> GetOrFetchObject <T>(this IBlobCache This, string key, Func <IObservable <T> > fetchFunc, DateTimeOffset?absoluteExpiration = null)
{
return(This.GetObject <T>(key).Catch <T, Exception>(_ =>
{
object dontcare;
var prefixedKey = This.GetHashCode().ToString() + key;
var result = Observable.Defer(() => fetchFunc())
.Do(x => This.InsertObject(key, x, absoluteExpiration))
.Finally(() => inflightFetchRequests.TryRemove(prefixedKey, out dontcare))
.Multicast(new AsyncSubject <T>()).RefCount();
return (IObservable <T>)inflightFetchRequests.GetOrAdd(prefixedKey, result);
}));
}
