Looping through keys in ASP.NET cache object

Question

Caching in ASP.NET looks like it uses some kind of associative array:

// Insert some data into the cache:
Cache.Insert("TestCache", someValue);
// Retrieve the data like normal:
someValue = Cache.Get("TestCache");

// But, can be done associatively ...
someValue = Cache["TestCache"];

// Also, null checks can be performed to see if cache exists yet:
if(Cache["TestCache"] == null) {
    Cache.Insert(PerformComplicatedFunctionThatNeedsCaching());
}
someValue = Cache["TestCache"];

As you can see, performing a null check on the cache object is very useful.

But I would like to implement a cache clear function that can clear cache values where I don't know the whole key name. As there seems to be an associative array here, it should be possible (?)

Can anyone help me work out a way of looping through the stored cache keys and performing simple logic on them? Here's what I'm after:

static void DeleteMatchingCacheKey(string keyName) {
    // This foreach implementation doesn't work by the way ...
    foreach(Cache as c) {
        if(c.Key.Contains(keyName)) {
            Cache.Remove(c);
        }
    }
}

The cache is under your control - why wouldn't you know the names of things that are in there? — Graham Clark, Nov 29 '10 at 10:49

score 5 · Accepted Answer · edited Feb 05 '14 at 19:11

5

Don't use a foreach loop when removing items from any collection type- the foreach loop relies on using an enumerator which will NOT allow you to remove items from the collection (the enumerator will throw an exception if the collection it is iterating over has items added or removed from it).

Use a simple while to loop over the cache keys instead:

int i = 0;
while (i < Cache.Keys.Length){
   if (Cache.Keys(i).Contains(keyName){
      Cache.Remove(Cache.Keys(i))
   } 
   else{
      i ++;
   }
}

edited Feb 05 '14 at 19:11

drzaus

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answered Nov 29 '10 at 10:48

WiseGuyEh

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Is this thread-safe? What if another thread is modifying the cache (e.g. adding and/or removing things from the cache) while this code is running? – Jon Schneider May 05 '15 at 20:04
1

The Cache class is thread safe so this code won't throw an exception. However, it might not remove all items from the cache if Cache.Add() is called after the last check of Cache.Keys.Length. – WiseGuyEh May 06 '15 at 09:08

Yanga · Answer 2 · 2019-11-02T16:09:14.560

0

An other way to do it in .net core:

var keys = _cache.Get<List<string>>(keyName);
foreach (var key in keys)
{
   _cache.Remove(key);
}

edited Nov 02 '19 at 16:09

answered Nov 02 '19 at 15:52

Yanga

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Looping through keys in ASP.NET cache object

2 Answers2