How to invalidate a single data item in the .net cache in VB

I have the following VB.NET code to set and read objects in cache on a per user basis (i.e. a bit like session)

Public Shared Sub CacheSet(ByVal Key As String, ByVal Value As Object)
    Dim userID As String = HttpContext.Current.User.Identity.Name

    HttpContext.Current.Cache(Key & "_" & userID) = Value
End Sub

Public Shared Function CacheGet(ByVal Key As Object)

    Dim returnData As Object = Nothing
    Dim userID As String = HttpContext.Current.User.Identity.Name

    returnData = HttpContext.Current.Cache(Key & "_" & userID)

    Return returnData

End Function

I use these functions to hold user开发者_如何学C data that I don't want to access the DB for all the time. However, when the data is updated, I want the cached item to be removed so it get created again.

How do I make an Item I set disappear or set it to NOTHING or NULL?

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Taking an item out of the cache is as simple as calling HttpContext.Current.Cache.Remove(Key) so in your case you'd probably want:

Public Shared Sub CacheRemove(ByVal key As String)

    Dim userID As String = HttpContext.Current.User.Identity.Name

    HttpContext.Current.Cache.Remove(Key & "_" & UserID)

End Sub

Since you say that when the data is updated you want the cached item to be removed so it gets re-cached with the updated data, you might want to take a look at using a SqlCacheDependency object. This wires up the cache to your database so that when your data changes, the cached item is automatically updated to keep it in sync.