Inserting Data into the Cache

There are several ways to add items into the Cache API:

Dictionary style-Similar to the way the Session or Application API is used.

Insert method-Inserts the named item into the cache and allows for additional

parameters that specify other cache behavior, such as when the item should be

removed from the cache.

Add method-Same as insert, but adds the item only if it did not already exist.

In the following examples, products is assumed to be a dataset. However, it could be

any .NET class.

' Add an item using the dictionary style API

Cache("MyProducts") = products

' Insert an item using the overloaded Insert method

Cache.Insert("MyProducts", products)

' Insert an item and specify a cache dependency

Cache.Insert("MyProducts", products, cacheDependency)

' Insert an item and specify that the item exists for only 60 minutes

Cache.Insert("MyProducts", products, Nothing,

DateTime.Now.AddMinutes(60), TimeSpan.Zero)

' Insert an item and specify that the item exists for only 60 minutes, has a

' high priority and specify a callback function called when the item is

' removed from the cache

Cache.Insert("MyProducts", products, Nothing, DateTime.Now.AddMinutes(60),

TimeSpan.Zero, CacheItemPriority.High, cacheCallBack)

' Add an item using the Add method

Cache.Add("MyProducts", products, cacheDependency,

DateTime.Now.AddMinutes(60), TimeSpan.Zero,

CacheItemPriority.High, cacheCallBack)

Comments

The Cache API, accessible simply as the Cache property within an ASP.NET page, is the

underlying data store used by page output caching, partial page caching, and Web service

caching.There are many cases when caching the output of the page is not desirable, but

data can still be reused. One example is a listing of products or reports.The data is stored

in memory, but options within the page determine how the data is displayed.

Something to keep in mind when using the cache is that it is scavenging.As memory is

needed, items are removed from the cache using an LRU (least recently used) algorithm.

Therefore, before using an item from the cache it is always wise to verify that the item

exists and is not Nothing:

If (Cache("MyProducts") Is Not Nothing)

… Insert into the cache

End If

The various parameters accepted by Insert() and Add() provide control over how the

cache stores data.You can provide a CacheDependency, which then enforces a relationship

between the item stored within the cache and either a file or cache key.When the

file or cache key changes, the related entry within the cache is removed. It is also possible

to specify time-based constraints using a fixed point in time or a sliding window of

time. It's possible to control the priority of items stored within the cache using the

CacheItemPriority enumeration-this affects how the scavenging algorithm removes

items. Finally, you can specify a callback function that the cache will call when an item is

removed.