/// <summary>
/// Fetches an item through cache - if the item exists and satisfies the `ICacheParams` (and optional `fFilter` functor) then it is immediately returned
/// to the caller. Otherwise, calls the `fFetch` functor to perform the actual fetch of a value by key, and then puts the result in cache
/// according to `ICacheParams`
/// </summary>
/// <typeparam name="TKey">Type of key</typeparam>
/// <typeparam name="TResult">Type of the result value</typeparam>
/// <param name="cache">Non-null ICache instance to operate on</param>
/// <param name="key">Key value</param>
/// <param name="tblCache">Name of cache table</param>
/// <param name="caching">Caching options, or null for defaults</param>
/// <param name="fFetch">Required functor that performs actual fetch when the value is NOT found in cache</param>
/// <param name="fFilter">Optional functor - additional filter applied to existing values</param>
/// <returns>Cached reference type value, or null if not found or absent</returns>
public static TResult FetchThrough <TKey, TResult>(this ICache cache,
TKey key,
string tblCache,
ICacheParams caching,
Func <TKey, TResult> fFetch,
Func <TKey, TResult, TResult> fFilter = null) where TResult : class
{
cache.NonNull(nameof(cache));
ICacheTable <TKey> tbl = null;
if (caching == null)
{
caching = CacheParams.DefaultCache;
}
if (caching.ReadCacheMaxAgeSec >= 0 || caching.WriteCacheMaxAgeSec >= 0)
{
tbl = cache.GetOrCreateTable <TKey>(tblCache);
}
TResult result = null;
if (caching.ReadCacheMaxAgeSec >= 0)
{
var cached = tbl.Get(key, caching.ReadCacheMaxAgeSec);
if (cached is AbsentValue)
{
return(null);
}
else
{
result = cached as TResult;
}
if (fFilter != null)
{
result = fFilter(key, result);
}
}
if (result != null)
{
return(result);
}
result = fFetch.NonNull(nameof(fFetch))(key);
if (result == null && !caching.CacheAbsentData)
{
return(null);
}
var wAge = caching.WriteCacheMaxAgeSec;
if (wAge >= 0)
{
tbl.Put(key, (object)result ?? AbsentValue.Instance, wAge > 0 ? wAge : (int?)null, caching.WriteCachePriority);
}
return(result);
}
public CustomDataReader(ICacheTable chacheTable)
{
_chacheTable = chacheTable;
_this = this;
}
/// <summary>
/// Asynchronously fetches an item through cache - if the item exists and satisfies the `ICacheParams` (and optional `fFilter` functor) then it is
/// immediately (synchronously) returned to the caller. Otherwise, calls the `fFetch` async functor to perform the actual fetch of a value by key,
/// and then puts the result in cache according to `ICacheParams`
/// </summary>
/// <typeparam name="TKey">Type of key</typeparam>
/// <typeparam name="TResult">Type of the result value</typeparam>
/// <param name="cache">Non-null ICache instance to operate on</param>
/// <param name="key">Key value</param>
/// <param name="tblCache">Name of cache table</param>
/// <param name="caching">Caching options, or null for defaults</param>
/// <param name="fFetch">Required async functor that performs actual fetch when the value is NOT found in cache</param>
/// <param name="fFilter">Optional functor - additional filter applied to existing values</param>
/// <param name="extraPut">Optional functor (cache, TKey, TResult, ICacheParams) which can be used to add the piled value to other cache tables (indexes) </param>
/// <returns>Cached reference type value, or null if not found or absent</returns>
public static async Task <TResult> FetchThroughAsync <TKey, TResult>(this ICache cache,
TKey key,
string tblCache,
ICacheParams caching,
Func <TKey, Task <TResult> > fFetch,
Func <TKey, TResult, TResult> fFilter = null,
Action <ICache, TKey, TResult, ICacheParams> extraPut = null
) where TResult : class
{
cache.NonNull(nameof(cache));
ICacheTable <TKey> tbl = null;
if (caching == null)
{
caching = CacheParams.DefaultCache;
}
if (caching.ReadCacheMaxAgeSec >= 0 || caching.WriteCacheMaxAgeSec >= 0)
{
tbl = cache.GetOrCreateTable <TKey>(tblCache);
}
TResult result = null;
if (caching.ReadCacheMaxAgeSec >= 0)
{
var cached = tbl.Get(key, caching.ReadCacheMaxAgeSec);
if (cached is AbsentValue)
{
return(null);
}
else
{
result = cached as TResult;
}
if (fFilter != null)
{
result = fFilter(key, result);
}
}
if (result != null)
{
return(result);
}
result = await fFetch.NonNull(nameof(fFetch))(key);//<-- only fFetch is IO-bound hence asynchronous
if (result == null && !caching.CacheAbsentData)
{
return(null);
}
var wAge = caching.WriteCacheMaxAgeSec;
if (wAge >= 0)
{
var pr = tbl.Put(key, (object)result ?? AbsentValue.Instance, out var ptr, wAge > 0 ? wAge : (int?)null, caching.WriteCachePriority);
if (pr != PutResult.Collision && ptr.Valid)
{
extraPut?.Invoke(cache, key, result, caching);
}
}
return(result);
}
public ExpressionDataReader(ICacheTable chacheTable, IExpression expression)
{
_chacheTable = chacheTable;
_expression = expression;
_this = this;
}
