/// <summary>
/// This method attempts to returned a cached value, while
/// simultaneously calling a Func to return the latest value. When the
/// latest data comes back, it replaces what was previously in the
/// cache.
///
/// This method is best suited for loading dynamic data from the
/// Internet, while still showing the user earlier data.
///
/// This method returns an IObservable that may return *two* results
/// (first the cached data, then the latest data). Therefore, it's
/// important for UI applications that in your Subscribe method, you
/// write the code to merge the second result when it comes in.
/// </summary>
/// <param name="key">The key to store the returned result under.</param>
/// <param name="fetchFunc"></param>
/// <param name="fetchPredicate">An optional Func to determine whether
/// the updated item should be fetched. If the cached version isn't found,
/// this parameter is ignored and the item is always fetched.</param>
/// <param name="absoluteExpiration">An optional expiration date.</param>
/// <returns>An Observable stream containing either one or two
/// results (possibly a cached version, then the latest version)</returns>
public static IObservable <T> GetAndFetchLatest <T>(this IBlobCache This,
string key,
Func <IObservable <T> > fetchFunc,
Func <DateTimeOffset, bool> fetchPredicate = null,
DateTimeOffset?absoluteExpiration = null)
{
bool foundItemInCache;
var fail = Observable.Defer(() => This.GetCreatedAt(key))
.Select(x => fetchPredicate != null && x != null ? fetchPredicate(x.Value) : true)
.Where(x => x != false)
.SelectMany(_ => fetchFunc())
.Finally(() => This.Invalidate(key))
.Do(x => This.InsertObject(key, x, absoluteExpiration));
var result = This.GetObjectAsync <T>(key).Select(x => new Tuple <T, bool>(x, true))
.Catch(Observable.Return(new Tuple <T, bool>(default(T), false)));
return(result.SelectMany(x =>
{
foundItemInCache = x.Item2;
return x.Item2 ?
Observable.Return(x.Item1) :
Observable.Empty <T>();
}).Concat(fail).Multicast(new ReplaySubject <T>()).RefCount());
}
/// <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.GetObjectAsync <T>(key).Catch <T, Exception>(_ =>
{
object dontcare;
return ((IObservable <T>)inflightFetchRequests.GetOrAdd(key, __ => (object)fetchFunc()))
.Do(x => This.InsertObject(key, x, absoluteExpiration))
.Finally(() => inflightFetchRequests.TryRemove(key, out dontcare))
.Multicast(new AsyncSubject <T>()).RefCount();
}));
}
/// <summary>
/// Return all objects of a specific Type in the cache.
/// </summary>
/// <returns>A Future result representing all objects in the cache
/// with the specified Type.</returns>
public static IObservable <IEnumerable <T> > GetAllObjects <T>(this IBlobCache This)
{
// NB: This isn't exactly thread-safe, but it's Close Enough(tm)
// We make up for the fact that the keys could get kicked out
// from under us via the Catch below
var matchingKeys = This.GetAllKeys()
.Where(x => x.StartsWith(GetTypePrefixedKey("", typeof(T))))
.ToArray();
return(matchingKeys.ToObservable()
.SelectMany(x => This.GetObjectAsync <T>(x, true).Catch(Observable.Empty <T>()))
.ToList()
.Select(x => (IEnumerable <T>)x));
}
/// <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.GetObjectAsync <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);
}));
}
public static IObservable <IDictionary <string, T> > GetObjectsAsync <T>(this IBlobCache This, IEnumerable <string> keys, bool noTypePrefix = false)
{
var bulkCache = This as IObjectBulkBlobCache;
if (bulkCache != null)
{
return(bulkCache.GetObjectsAsync <T>(keys));
}
return(keys.ToObservable()
.SelectMany(x =>
{
return This.GetObjectAsync <T>(x)
.Select(y => new KeyValuePair <string, T>(x, y))
.Catch <KeyValuePair <string, T>, KeyNotFoundException>(_ => Observable.Empty <KeyValuePair <string, T> >());
})
.ToDictionary(k => k.Key, v => v.Value));
}
/// <summary>
/// Return all objects of a specific Type in the cache.
/// </summary>
/// <returns>A Future result representing all objects in the cache
/// with the specified Type.</returns>
public static IObservable <IEnumerable <T> > GetAllObjects <T>(this IBlobCache This)
{
var objCache = This as IObjectBlobCache;
if (objCache != null)
{
return(objCache.GetAllObjects <T>());
}
// NB: This isn't exactly thread-safe, but it's Close Enough(tm)
// We make up for the fact that the keys could get kicked out
// from under us via the Catch below
var matchingKeys = This.GetAllKeys()
.ToArray();
return(matchingKeys.ToObservable()
.SelectMany(x => This.GetObjectAsync <T>(x, true).Catch(Observable.Empty <T>()))
.ToList()
.Where(x => x is T)
.Select(x => (IEnumerable <T>)x));
}
/// <summary>
/// This method attempts to returned a cached value, while
/// simultaneously calling a Func to return the latest value. When the
/// latest data comes back, it replaces what was previously in the
/// cache.
///
/// This method is best suited for loading dynamic data from the
/// Internet, while still showing the user earlier data.
///
/// This method returns an IObservable that may return *two* results
/// (first the cached data, then the latest data). Therefore, it's
/// important for UI applications that in your Subscribe method, you
/// write the code to merge the second result when it comes in.
///
/// This also means that await'ing this method is a Bad Idea(tm), always
/// use Subscribe.
/// </summary>
/// <param name="key">The key to store the returned result under.</param>
/// <param name="fetchFunc"></param>
/// <param name="fetchPredicate">An optional Func to determine whether
/// the updated item should be fetched. If the cached version isn't found,
/// this parameter is ignored and the item is always fetched.</param>
/// <param name="absoluteExpiration">An optional expiration date.</param>
/// <param name="shouldInvalidateOnError">If this is true, the cache will
/// be cleared when an exception occurs in fetchFunc</param>
/// <returns>An Observable stream containing either one or two
/// results (possibly a cached version, then the latest version)</returns>
public static IObservable <T> GetAndFetchLatest <T>(this IBlobCache This,
string key,
Func <IObservable <T> > fetchFunc,
Func <DateTimeOffset, bool> fetchPredicate = null,
DateTimeOffset?absoluteExpiration = null,
bool shouldInvalidateOnError = false)
{
var fetch = Observable.Defer(() => This.GetObjectCreatedAt <T>(key))
.Select(x => fetchPredicate == null || x == null || fetchPredicate(x.Value))
.Where(x => x != false)
.SelectMany(async _ => {
var ret = default(T);
try {
ret = await fetchFunc();
} catch (Exception) {
if (shouldInvalidateOnError)
{
This.InvalidateObject <T>(key);
}
throw;
}
await This.InvalidateObject <T>(key);
await This.InsertObject(key, ret, absoluteExpiration);
return(ret);
});
var result = This.GetObjectAsync <T>(key).Select(x => new Tuple <T, bool>(x, true))
.Catch(Observable.Return(new Tuple <T, bool>(default(T), false)));
return(result.SelectMany(x =>
{
return x.Item2 ?
Observable.Return(x.Item1) :
Observable.Empty <T>();
}).Concat(fetch).Multicast(new ReplaySubject <T>()).RefCount());
}