Since IMemoryCache does not give too much info about the cached items I was thinking to implement something custom in order to keep some data about items in the cache like the key, AbsoluteExpiration properties etc.
Here is my implementation of IMemoryCache:
public class MemoryCacheService : IMemoryCache
{
private readonly MemoryCache _memoryCache;
private readonly List<CacheItemRelevantData> _allKeys;
private readonly string AllKeys = "___All__Keys___";
public MemoryCacheService()
{
_memoryCache = new MemoryCache(new MemoryCacheOptions());
_allKeys = new List<CacheItemRelevantData>();
_memoryCache.Set(AllKeys, _allKeys, new MemoryCacheEntryOptions
{
AbsoluteExpiration = DateTimeOffset.MaxValue
});
}
public void Dispose()
{
_memoryCache.Dispose();
}
public bool TryGetValue(object key, out object value)
{
return _memoryCache.TryGetValue(key, out value);
}
public ICacheEntry CreateEntry(object key)
{
var entry = _memoryCache.CreateEntry(key);
entry.RegisterPostEvictionCallback((o, v, reason, state) =>
{
if (reason.In(EvictionReason.Capacity, EvictionReason.Expired, EvictionReason.TokenExpired))
{
var item = _allKeys.FirstOrDefault(x => x.Key.ToString() == o.ToString());
if (item != null)
{
_allKeys.Remove(item);
}
}
});
if (!_allKeys.Select(x => x.Key).Contains(key))
{
_allKeys.Add(new CacheItemRelevantData
{
Key = entry.Key,
AbsoluteExpiration = entry.AbsoluteExpiration,
Priority = entry.Priority,
AbsoluteExpirationRelativeToNow = entry.AbsoluteExpirationRelativeToNow,
Size = entry.Size
});
}
return entry;
}
public void Remove(object key)
{
var entry = _allKeys.FirstOrDefault(x => x.Key.ToString() == key.ToString());
if (entry != null)
{
_allKeys.Remove(entry);
}
_memoryCache.Remove(key);
}
}
But since _allKeys is created to store the relevant data about cached items I dont want it to expire.
Is there any way to set expire time to none or something similar and the _allKeys list will remain in cache forever ?
For my case I could easily solve the problem because the IMemoryService was configured as scoped service and that means _allKeys variable is persisting in memory as far IMemoryService instance(until the iis is restarted or something). For non-scoped service I did not find a proper solution but I think IMemoryCache service should always be a scoped service(there is no real case to have it configured differently -maybe!!)
I have read lots of information about page caching and partial page caching in a MVC application. However, I would like to know how you would cache data.
In my scenario I will be using LINQ to Entities (entity framework). On the first call to GetNames (or whatever the method is) I want to grab the data from the database. I want to save the results in cache and on the second call to use the cached version if it exists.
Can anyone show an example of how this would work, where this should be implemented (model?) and if it would work.
I have seen this done in traditional ASP.NET apps , typically for very static data.
Here's a nice and simple cache helper class/service I use:
using System.Runtime.Caching;
public class InMemoryCache: ICacheService
{
public T GetOrSet<T>(string cacheKey, Func<T> getItemCallback) where T : class
{
T item = MemoryCache.Default.Get(cacheKey) as T;
if (item == null)
{
item = getItemCallback();
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.AddMinutes(10));
}
return item;
}
}
interface ICacheService
{
T GetOrSet<T>(string cacheKey, Func<T> getItemCallback) where T : class;
}
Usage:
cacheProvider.GetOrSet("cache key", (delegate method if cache is empty));
Cache provider will check if there's anything by the name of "cache id" in the cache, and if there's not, it will call a delegate method to fetch data and store it in cache.
Example:
var products=cacheService.GetOrSet("catalog.products", ()=>productRepository.GetAll())
Reference the System.Web dll in your model and use System.Web.Caching.Cache
public string[] GetNames()
{
string[] names = Cache["names"] as string[];
if(names == null) //not in cache
{
names = DB.GetNames();
Cache["names"] = names;
}
return names;
}
A bit simplified but I guess that would work. This is not MVC specific and I have always used this method for caching data.
I'm referring to TT's post and suggest the following approach:
Reference the System.Web dll in your model and use System.Web.Caching.Cache
public string[] GetNames()
{
var noms = Cache["names"];
if(noms == null)
{
noms = DB.GetNames();
Cache["names"] = noms;
}
return ((string[])noms);
}
You should not return a value re-read from the cache, since you'll never know if at that specific moment it is still in the cache. Even if you inserted it in the statement before, it might already be gone or has never been added to the cache - you just don't know.
So you add the data read from the database and return it directly, not re-reading from the cache.
For .NET 4.5+ framework
add reference: System.Runtime.Caching
add using statement:
using System.Runtime.Caching;
public string[] GetNames()
{
var noms = System.Runtime.Caching.MemoryCache.Default["names"];
if(noms == null)
{
noms = DB.GetNames();
System.Runtime.Caching.MemoryCache.Default["names"] = noms;
}
return ((string[])noms);
}
In the .NET Framework 3.5 and earlier versions, ASP.NET provided an in-memory cache implementation in the System.Web.Caching namespace. In previous versions of the .NET Framework, caching was available only in the System.Web namespace and therefore required a dependency on ASP.NET classes. In the .NET Framework 4, the System.Runtime.Caching namespace contains APIs that are designed for both Web and non-Web applications.
More info:
https://msdn.microsoft.com/en-us/library/dd997357(v=vs.110).aspx
https://learn.microsoft.com/en-us/dotnet/framework/performance/caching-in-net-framework-applications
Steve Smith did two great blog posts which demonstrate how to use his CachedRepository pattern in ASP.NET MVC. It uses the repository pattern effectively and allows you to get caching without having to change your existing code.
http://ardalis.com/Introducing-the-CachedRepository-Pattern
http://ardalis.com/building-a-cachedrepository-via-strategy-pattern
In these two posts he shows you how to set up this pattern and also explains why it is useful. By using this pattern you get caching without your existing code seeing any of the caching logic. Essentially you use the cached repository as if it were any other repository.
I have used it in this way and it works for me.
https://msdn.microsoft.com/en-us/library/system.web.caching.cache.add(v=vs.110).aspx
parameters info for system.web.caching.cache.add.
public string GetInfo()
{
string name = string.Empty;
if(System.Web.HttpContext.Current.Cache["KeyName"] == null)
{
name = GetNameMethod();
System.Web.HttpContext.Current.Cache.Add("KeyName", name, null, DateTime.Noew.AddMinutes(5), Cache.NoSlidingExpiration, CacheitemPriority.AboveNormal, null);
}
else
{
name = System.Web.HttpContext.Current.Cache["KeyName"] as string;
}
return name;
}
AppFabric Caching is distributed and an in-memory caching technic that stores data in key-value pairs using physical memory across multiple servers. AppFabric provides performance and scalability improvements for .NET Framework applications. Concepts and Architecture
Extending #Hrvoje Hudo's answer...
Code:
using System;
using System.Runtime.Caching;
public class InMemoryCache : ICacheService
{
public TValue Get<TValue>(string cacheKey, int durationInMinutes, Func<TValue> getItemCallback) where TValue : class
{
TValue item = MemoryCache.Default.Get(cacheKey) as TValue;
if (item == null)
{
item = getItemCallback();
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.AddMinutes(durationInMinutes));
}
return item;
}
public TValue Get<TValue, TId>(string cacheKeyFormat, TId id, int durationInMinutes, Func<TId, TValue> getItemCallback) where TValue : class
{
string cacheKey = string.Format(cacheKeyFormat, id);
TValue item = MemoryCache.Default.Get(cacheKey) as TValue;
if (item == null)
{
item = getItemCallback(id);
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.AddMinutes(durationInMinutes));
}
return item;
}
}
interface ICacheService
{
TValue Get<TValue>(string cacheKey, Func<TValue> getItemCallback) where TValue : class;
TValue Get<TValue, TId>(string cacheKeyFormat, TId id, Func<TId, TValue> getItemCallback) where TValue : class;
}
Examples
Single item caching (when each item is cached based on its ID because caching the entire catalog for the item type would be too intensive).
Product product = cache.Get("product_{0}", productId, 10, productData.getProductById);
Caching all of something
IEnumerable<Categories> categories = cache.Get("categories", 20, categoryData.getCategories);
Why TId
The second helper is especially nice because most data keys are not composite. Additional methods could be added if you use composite keys often. In this way you avoid doing all sorts of string concatenation or string.Formats to get the key to pass to the cache helper. It also makes passing the data access method easier because you don't have to pass the ID into the wrapper method... the whole thing becomes very terse and consistant for the majority of use cases.
Here's an improvement to Hrvoje Hudo's answer. This implementation has a couple of key improvements:
Cache keys are created automatically based on the function to update data and the object passed in that specifies dependencies
Pass in time span for any cache duration
Uses a lock for thread safety
Note that this has a dependency on Newtonsoft.Json to serialize the dependsOn object, but that can be easily swapped out for any other serialization method.
ICache.cs
public interface ICache
{
T GetOrSet<T>(Func<T> getItemCallback, object dependsOn, TimeSpan duration) where T : class;
}
InMemoryCache.cs
using System;
using System.Reflection;
using System.Runtime.Caching;
using Newtonsoft.Json;
public class InMemoryCache : ICache
{
private static readonly object CacheLockObject = new object();
public T GetOrSet<T>(Func<T> getItemCallback, object dependsOn, TimeSpan duration) where T : class
{
string cacheKey = GetCacheKey(getItemCallback, dependsOn);
T item = MemoryCache.Default.Get(cacheKey) as T;
if (item == null)
{
lock (CacheLockObject)
{
item = getItemCallback();
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.Add(duration));
}
}
return item;
}
private string GetCacheKey<T>(Func<T> itemCallback, object dependsOn) where T: class
{
var serializedDependants = JsonConvert.SerializeObject(dependsOn);
var methodType = itemCallback.GetType();
return methodType.FullName + serializedDependants;
}
}
Usage:
var order = _cache.GetOrSet(
() => _session.Set<Order>().SingleOrDefault(o => o.Id == orderId)
, new { id = orderId }
, new TimeSpan(0, 10, 0)
);
public sealed class CacheManager
{
private static volatile CacheManager instance;
private static object syncRoot = new Object();
private ObjectCache cache = null;
private CacheItemPolicy defaultCacheItemPolicy = null;
private CacheEntryRemovedCallback callback = null;
private bool allowCache = true;
private CacheManager()
{
cache = MemoryCache.Default;
callback = new CacheEntryRemovedCallback(this.CachedItemRemovedCallback);
defaultCacheItemPolicy = new CacheItemPolicy();
defaultCacheItemPolicy.AbsoluteExpiration = DateTime.Now.AddHours(1.0);
defaultCacheItemPolicy.RemovedCallback = callback;
allowCache = StringUtils.Str2Bool(ConfigurationManager.AppSettings["AllowCache"]); ;
}
public static CacheManager Instance
{
get
{
if (instance == null)
{
lock (syncRoot)
{
if (instance == null)
{
instance = new CacheManager();
}
}
}
return instance;
}
}
public IEnumerable GetCache(String Key)
{
if (Key == null || !allowCache)
{
return null;
}
try
{
String Key_ = Key;
if (cache.Contains(Key_))
{
return (IEnumerable)cache.Get(Key_);
}
else
{
return null;
}
}
catch (Exception)
{
return null;
}
}
public void ClearCache(string key)
{
AddCache(key, null);
}
public bool AddCache(String Key, IEnumerable data, CacheItemPolicy cacheItemPolicy = null)
{
if (!allowCache) return true;
try
{
if (Key == null)
{
return false;
}
if (cacheItemPolicy == null)
{
cacheItemPolicy = defaultCacheItemPolicy;
}
String Key_ = Key;
lock (Key_)
{
return cache.Add(Key_, data, cacheItemPolicy);
}
}
catch (Exception)
{
return false;
}
}
private void CachedItemRemovedCallback(CacheEntryRemovedArguments arguments)
{
String strLog = String.Concat("Reason: ", arguments.RemovedReason.ToString(), " | Key-Name: ", arguments.CacheItem.Key, " | Value-Object: ", arguments.CacheItem.Value.ToString());
LogManager.Instance.Info(strLog);
}
}
I use two classes. First one the cache core object:
public class Cacher<TValue>
where TValue : class
{
#region Properties
private Func<TValue> _init;
public string Key { get; private set; }
public TValue Value
{
get
{
var item = HttpRuntime.Cache.Get(Key) as TValue;
if (item == null)
{
item = _init();
HttpContext.Current.Cache.Insert(Key, item);
}
return item;
}
}
#endregion
#region Constructor
public Cacher(string key, Func<TValue> init)
{
Key = key;
_init = init;
}
#endregion
#region Methods
public void Refresh()
{
HttpRuntime.Cache.Remove(Key);
}
#endregion
}
Second one is list of cache objects:
public static class Caches
{
static Caches()
{
Languages = new Cacher<IEnumerable<Language>>("Languages", () =>
{
using (var context = new WordsContext())
{
return context.Languages.ToList();
}
});
}
public static Cacher<IEnumerable<Language>> Languages { get; private set; }
}
I will say implementing Singleton on this persisting data issue can be a solution for this matter in case you find previous solutions much complicated
public class GPDataDictionary
{
private Dictionary<string, object> configDictionary = new Dictionary<string, object>();
/// <summary>
/// Configuration values dictionary
/// </summary>
public Dictionary<string, object> ConfigDictionary
{
get { return configDictionary; }
}
private static GPDataDictionary instance;
public static GPDataDictionary Instance
{
get
{
if (instance == null)
{
instance = new GPDataDictionary();
}
return instance;
}
}
// private constructor
private GPDataDictionary() { }
} // singleton
HttpContext.Current.Cache.Insert("subjectlist", subjectlist);
You can also try and use the caching built into ASP MVC:
Add the following attribute to the controller method you'd like to cache:
[OutputCache(Duration=10)]
In this case the ActionResult of this will be cached for 10 seconds.
More on this here
I have the following cache implementation for my application:
public static class Keys
{
public const string CacheKey = "cachekey";
}
public interface ICache
{
string QueryCachedData(string param);
}
the data is loaded when the application starts in Global.asax
//Global.asax
protected void Application_Start(object sender, EventArgs e)
{
//instantiates the repository
HttpContext.Current.Application[Keys.CacheKey] = repository.getDataView();
}
the implementation recover the data from HttpContext.Current
public class Cache : ICache
{
private Cache() { }
private static Cache _instance = null;
public static Cache GetInstance()
{
if (_instance == null)
_instance = new Cache();
return _instance;
}
private System.Data.DataView GetCachedData()
{
if (HttpContext.Current.Application[Keys.CacheKey] == null)
{
//instantiates the repository
HttpContext.Current.Application[Keys.CacheKey] = repository.getDataView();
}
return HttpContext.Current.Application[Keys.CacheKey] as System.Data.DataView;
}
private readonly Object _lock = new Object();
public string QueryCachedData(string param)
{
lock (_lock)
{
var data = GetCachedData();
//Execute query
return result;
}
}
}
at some point i need consume some third party web service with the following class using the cache...
public class ThirdPartyWebserviceConsumer
{
ICache _cache;
int _provider;
public ThirdPartyWebserviceConsumer(int provider, ICache cache)
{
_cache = cache;
_provider = provider;
}
public result DoSomething()
{
var info = _cache.QueryCachedData(param);
}
}
...using multi-thread:
public List<Result> Foo(ICache cache, List<int> collectionOfProviders)
{
List<Result> results = new List<Result>();
List<Task> taskList = new List<Task>();
foreach (var provider in collectionOfProviders)
{
var task = new Task<Result>(() => new ThirdPartyWebserviceConsumer(provider, cache).DoSomething());
task.Start();
task.ContinueWith(task =>
{
results.Add(task.Result);
});
taskList.Add(task);
}
Task.WaitAll(taskList.ToArray());
return results;
}
My problem is that HttpContext.Current.Application is null in the thead context.
What options do I have? there are some form to access the HttpContext in thread? or maybe another type of cache that could be shared between the threads?
My problem is that HttpContext.Current.Application is null in the thead context. What options do I have?
HttpContext.Current is bound to the managed thread processing the current request.
If you need data from the current context for another thread, you need to copy that data out of the current context first and pass it to your separate thread.
Im new to generics in c#, and I'm trying to create a storage that other parts of my program can ask for models objects.
The idea was that if my cache class has the object, it checks its date and returns it if the object is not older then 10 min.
If it is older then 10 min it downloads a updated model from the server online.
It it does not have the object is downloads it and returns it.
But I'm having some problems pairing my objects with a DateTime, makeing it all generic.
// model
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
class Program
{
static void Main(string[] args)
{
Person p = new Person();
Cache c = new Cache();
p = c.Get<Person>(p);
}
}
public class Cache
{
struct DatedObject<T>
{
public DateTime Time { get; set; }
public T Obj { get; set; }
}
List<DatedObject<T>> objects;
public Cache()
{
objects = new List<DatedObject<T>>();
}
public T Get<T>(T obj)
{
bool found = false;
// search to see if the object is stored
foreach(var elem in objects)
if( elem.ToString().Equals(obj.ToString() ) )
{
// the object is found
found = true;
// check to see if it is fresh
TimeSpan sp = DateTime.Now - elem.Time;
if( sp.TotalMinutes <= 10 )
return elem;
}
// object was not found or out of date
// download object from server
var ret = JsonConvert.DeserializeObject<T>("DOWNLOADED JSON STRING");
if( found )
{
// redate the object and replace it in list
foreach(var elem in objects)
if( elem.Obj.ToString().Equals(obj.ToString() ) )
{
elem.Obj = ret;
elem.Time = DateTime.Now;
}
}
else
{
// add the object to the list
objects.Add( new DatedObject<T>() { Time = DateTime.Now, Obj = ret });
}
return ret;
}
}
Check out the memory cache class available as part of the .NET framework http://msdn.microsoft.com/en-us/library/system.runtime.caching.memorycache.aspx
You'll need to add the System.RunTime.Caching assembly as a reference to your application. The following is a helper class to add items and remove them from cache.
using System;
using System.Runtime.Caching;
public static class CacheHelper
{
public static void SaveTocache(string cacheKey, object savedItem, DateTime absoluteExpiration)
{
MemoryCache.Default.Add(cacheKey, savedItem, absoluteExpiration);
}
public static T GetFromCache<T>(string cacheKey) where T : class
{
return MemoryCache.Default[cacheKey] as T;
}
public static void RemoveFromCache(string cacheKey)
{
MemoryCache.Default.Remove(cacheKey);
}
public static bool IsIncache(string cacheKey)
{
return MemoryCache.Default[cacheKey] != null;
}
}
The nice thing about this is that it's thread safe, and it takes care of expiring the cache automatically for you. So basically all you have to do is check if getting an item from MemoryCache is null or not. Note however that MemoryCache is only available in .NET 4.0+
If your application is a web application then use System.Web.Caching rather than MemoryCache. System.Web.Caching has been available since .NET 1.1 and there's no additional references you have to add to your project. Heres the same helper class for web.
using System.Web;
public static class CacheHelper
{
public static void SaveTocache(string cacheKey, object savedItem, DateTime absoluteExpiration)
{
if (IsIncache(cacheKey))
{
HttpContext.Current.Cache.Remove(cacheKey);
}
HttpContext.Current.Cache.Add(cacheKey, savedItem, null, System.Web.Caching.Cache.NoAbsoluteExpiration, new TimeSpan(0, 10, 0), System.Web.Caching.CacheItemPriority.Default, null);
}
public static T GetFromCache<T>(string cacheKey) where T : class
{
return HttpContext.Current.Cache[cacheKey] as T;
}
public static void RemoveFromCache(string cacheKey)
{
HttpContext.Current.Cache.Remove(cacheKey);
}
public static bool IsIncache(string cacheKey)
{
return HttpContext.Current.Cache[cacheKey] != null;
}
}
There are other cache expiration policies that you can use for both of these patterns, for instance cache based on a file path(s) so that when a file changes the cache automatically expires, SQL cache dependency (does periodic polling of the SQL server for changes), sliding expiration or you could build your own. They come in really handy.
I would like to cache strings in memory from the database so that I do not have to access the database every time. I tried using System.Runtime.Caching, but it does not seem to work.
On the local site, all the data is cached but the user has to be authenticated on a secondary site. Once the user is authenticated, they are brought back to the local site but all the data that was cached is gone.
Is there a way to fix the above issue? Below is part of my code:
using System.Runtime.Caching;
ObjectCache cache = MemoryCache.Default;
public bool CacheIsSet(string key)
{
return cache.Contains(key);
}
public object CacheGet(string key)
{
return cache.Get(key);
}
public void CacheSet(string key, object value)
{
CacheItemPolicy policy = new CacheItemPolicy();
cache.Set(key, value, policy);
}
Thanks very much.
You should be referencing the HttpRuntime.Cache object. I created a wrapper around this, similar to what you have referenced in your question. Feel free to use it:
using System.Web.Caching;
public class CachingService
{
protected Cache Cache
{
get;
set;
}
public int CacheDurationMinutes
{
get;
set;
}
public CachingService()
{
Cache = HttpRuntime.Cache;
CacheDurationMinutes = 60;
}
public virtual object Get(string keyname)
{
return Cache[keyname];
}
public virtual T Get<T>(string keyname)
{
T item = (T)Cache[keyname];
return item;
}
public virtual void Insert(string keyname, object item)
{
Cache.Insert(keyname, item, null, DateTime.UtcNow.AddMinutes(CacheDurationMinutes), Cache.NoSlidingExpiration);
}
public virtual void Insert(string keyname, object item, CacheDependency dependency)
{
Cache.Insert(keyname, item, dependency);
}
public virtual void Remove(string keyname)
{
Cache.Remove(keyname);
}
}
Here is a sample use case. The function LoadPosts is supposed to load blog posts to display on the site. The function will first see if the posts are cached, if not it will load the posts from the database, and then cache them:
public IEnumerable<BlogPost> LoadPosts()
{
var cacheService = new CachingService();
var blogPosts = cacheService.Get<IEnumerable<BlogPost>>("BlogPosts");
if (blogPosts == null)
{
blogPosts = postManager.LoadPostsFromDatabase();
cacheService.Insert("BlogPosts", blogPosts);
}
return blogPosts;
}
The first time this function is run, the cache will return null, because we didn't add anything to the BlogPosts key yet. The second time the function is called the posts will be in the cache and the code in the if block will not run, saving us a trip to the database.