How to Get Items From Cache by Tag Without Knowing The Region

Question

We are using MS Velocity, and moving to AppFabric soon. We are interested in possibly using tags to retrieve items from the cache in the future. The Velocity/App Fabric API includes an add method that look like

public DataCacheItemVersion Add(string key, 
                                object value, 
                                IEnumerable<DataCacheTag> tags);

However, there are no methods available for retrieving objects from the cache using tags that do not require a region to be specified.

The problem is that if you use Add() without specifying the region, you have no idea what region the cache manager put the object into; thus you cannot specify the region when retrieving the object. Am I missing something really simple here?

score 2 · Answer 1 · answered Mar 15 '11 at 19:07

If you are using the DataCache class then there are several overloads available, including the first one which only specifies a key:

DataCache.Get (String) - Gets an object from the cache using the specified key.

DataCache.Get (String, out DataCacheItemVersion) - Gets an object from the cache using the specified key. You may also provide the version to obtain the specific version of a key, if that version is still the most current in the cache.

DataCache.Get (String, String) - Gets an object from the specified region by using the specified key.

DataCache.Get (String, out DataCacheItemVersion, String) - Gets an object from the specified region by using the specified key. You may also provide the version to obtain the specific version of a key, if that version is still the most current in the region.

from http://msdn.microsoft.com/en-us/library/microsoft.data.caching.datacache.get.aspx

score 2 · Accepted Answer · answered Mar 15 '11 at 21:36

I finally found the answer to my question in the MSDN. It can be seen here. As it turns out, when you call the overloaded Add() method (the one I originally posted) that accepts tags, you cannot retrieve the object based on the tags. The linked document states:

Tags may only be used to retrieve a cached object if that object is stored in a region. This overload does not store the object in a region.

So, using that overload, the tags essentially just become metadata.

Thanks for the other answers. I up-voted both of them, because they helped lead to me finding this answer.

score 1 · Answer 3 · edited May 23 '17 at 11:55

1

You can iterate through all regions, but it is not a very optimized way of getting data.

foreach (string regionName in cache.GetSystemRegions())
{
    string value = cache.Get(regionName, key);
}

But Get(key) should work for Add(key). See this question and answer for more info on iterating regions.

edited May 23 '17 at 11:55

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answered Mar 15 '11 at 20:18

Tedd Hansen

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How to Get Items From Cache by Tag Without Knowing The Region

3 Answers3