Creating a Cache Dependency

As discussed in Section 4.3, the cache allows for items to be inserted or added to the

Cache along with several other parameters, such as time-based constraints or an instance

of

CacheDependency.

<script runat="server">

Sub Page_Load(object As Sender, e As EventArgs)

Dim stringArray As string {"Rob", "Steve", "Mike", "Anne"}

' Time based dependency for 60 minutes

Cache.Insert("myArray-Time", stringArray, Nothing,

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

' File based dependency

Dim fileDep = New CacheDependency(Server.MapPath("Products.xml"))

Cache.Insert("myArray-File", stringArray, fileDep)

' Key based dependency

Cache.Insert("myKey", "key for dependencies")

Dim keyDep = New CacheDependency(Nothing, "myKey")

Cache.Insert("myArray-Key", stringArray, fileDep)

End Sub

</script>

Comments

In the previous examples, three types of dependencies are created:

n Time-Time-based dependencies specify that an item is to remain in the cache

for the specified duration of time.This is the same functionality found when using

the @OutputCache directive and setting the Duration attribute.

n File-File-based dependencies specify that an item is to remain in the cache until

the named file changes.Any output cached page is automatically made dependent

upon itself. However, it's possible-as demonstrated in this example-to use this

same functionality for entries within the Cache API.

n Key-Key-based dependencies specify that an item is to remain in the cache until

a related cache key changes.This is very powerful because any running ASP.NET

code can affect the cache key to enforce this relationship. For example, cascading

relationships can be established whereby one cache entry is changed or removed

and multiple other cache entries are affected.

Dependencies provide a simple but powerful programming model for controlling

removal of resources from the cache when other resources change.