AggregateCacheDependency Class

Definition

Namespace:

System.Web.Caching

Assembly:

System.Web.dll

Combines multiple dependencies between an item stored in an ASP.NET application's Cache object and an array of CacheDependency objects. This class cannot be inherited.

public ref class AggregateCacheDependency sealed : System::Web::Caching::CacheDependency

public sealed class AggregateCacheDependency : System.Web.Caching.CacheDependency

type AggregateCacheDependency = class
    inherit CacheDependency

Public NotInheritable Class AggregateCacheDependency
Inherits CacheDependency

Inheritance

Object

CacheDependency

AggregateCacheDependency

Examples

The following code example uses the AggregateCacheDependency class to add a DataSet, named XMLDataSet, to the cache that is dependent on a text file and an XML file.

   ' When the page is loaded, use the 
   ' AggregateCacheDependency class to make 
   ' a cached item dependent on two files.
   
   Sub Page_Load(sender As Object, e As EventArgs)
      Dim Source As DataView
   
      Source = Cache("XMLDataSet")
   
      If Source Is Nothing
             Dim DS As New DataSet
             Dim FS As FileStream
             Dim Reader As StreamReader
             Dim txtDep As CacheDependency
             Dim xmlDep As CacheDependency
             Dim aggDep As AggregateCacheDependency
   
   
             FS = New FileStream(Server.MapPath("authors.xml"),FileMode.Open,FileAccess.Read)
             Reader = New StreamReader(FS)
             DS.ReadXml(Reader)
             FS.Close()
   
             Source = new DataView(ds.Tables(0))
            ' Create two CacheDependency objects, one to a
            ' text file and the other to an XML file. 
            ' Create a CacheDependency array with these 
            ' two objects as items in the array.
             txtDep = New CacheDependency(Server.MapPath("Storage.txt"))
             xmlDep = New CacheDependency(Server.MapPath("authors.xml"))
             Dim DepArray() As CacheDependency = {txtDep, xmlDep}

             ' Create an AggregateCacheDependency object and 
             ' use the Add method to add the array to it.   
             aggDep = New AggregateCacheDependency()
             aggDep.Add(DepArray)
   
             ' Call the GetUniqueId method to generate
             ' an ID for each dependency in the array.
             msg1.Text = aggDep.GetUniqueId()
             
             ' Add the new data set to the cache with 
             ' dependencies on both files in the array.
             Cache.Insert("XMLDataSet", Source, aggDep)
             If aggDep.HasChanged = True Then
                chngMsg.Text = "The dependency changed at: " & DateTime.Now
   
             Else
                chngMsg.Text = "The dependency changed last at: " & aggDep.UtcLastModified.ToString()
             End If

   
             cacheMsg1.Text = "Dataset created explicitly"
           Else
             cacheMsg1.Text = "Dataset retrieved from cache"
           End If
   
   
             MyLiteral.Text = Source.Table.TableName
             MyDataGrid.DataSource = Source
             MyDataGrid.DataBind()
         End Sub
 

         Public Sub btn_Click(sender As Object, e As EventArgs )
   
          If (MyTextBox.Text = String.Empty) Then
             msg2.Text ="You have not changed the text file."
          Else
             msg2.Text="You added " & MyTextBox.Text & "."
   
             ' Create an instance of the StreamWriter class
             ' to write text to a file.
             Dim sw As StreamWriter
             sw = File.CreateText(Server.MapPath("Storage.txt"))
   
             ' Add some text to the file.
             sw.Write("You entered:")
             sw.WriteLine(MyTextBox.Text)
   
             ' Write arbitrary objects to the file as needed.
             sw.Write("Text added at:")
             sw.WriteLine(DateTime.Now)
             sw.WriteLine("-------------------")
             sw.Close()
          End If
        End Sub

Remarks

The AggregateCacheDependency class monitors a collection of dependency objects so that when any of them change, the cached item is automatically removed. The objects in the array can be CacheDependency objects, SqlCacheDependency objects, custom objects derived from CacheDependency, or any combination of these.

The AggregateCacheDependency class differs from the CacheDependency class in that it allows you to associate multiple dependencies of different types with a single cached item. For example, if you create a page that imports data from a SQL Server database table and an XML file, you can create a SqlCacheDependency object to represent a dependency on the database table and a CacheDependency to represent the dependency on the XML file. Rather than making an Cache.Insert method call for each dependency, you can create an instance of the AggregateCacheDependency class with each dependency added to it. You can then use a single Insert call to make the page dependent on the AggregateCacheDependency instance.

Constructors

AggregateCacheDependency()

Initializes a new instance of the AggregateCacheDependency class.

Properties

HasChanged	Gets a value indicating whether the CacheDependency object has changed. (Inherited from CacheDependency)
UtcLastModified	Gets the time when the dependency was last changed. (Inherited from CacheDependency)

Methods

Add(CacheDependency[])	Adds an array of CacheDependency objects to the AggregateCacheDependency object.
DependencyDispose()	Releases the resources used by the CacheDependency class and any classes that derive from CacheDependency. (Inherited from CacheDependency)
Dispose()	Releases the resources used by the CacheDependency object. (Inherited from CacheDependency)
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
FinishInit()	Completes initialization of the CacheDependency object. (Inherited from CacheDependency)
GetFileDependencies()	Gets the file dependencies.
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
GetUniqueID()	Retrieves a unique identifier for the AggregateCacheDependency object.
ItemRemoved()	Called when a monitored cache entry is removed. (Inherited from CacheDependency)
KeepDependenciesAlive()	Updates the last access time of every cache item that depends on this item. (Inherited from CacheDependency)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
NotifyDependencyChanged(Object, EventArgs)	Notifies the base CacheDependency object that the dependency represented by a derived CacheDependency class has changed. (Inherited from CacheDependency)
SetCacheDependencyChanged(Action<Object,EventArgs>)	Adds an Action method to handle notifying interested party in changes to this dependency. (Inherited from CacheDependency)
SetUtcLastModified(DateTime)	Marks the time when a dependency last changed. (Inherited from CacheDependency)
TakeOwnership()	Allows the first user to declare exclusive ownership of this dependency. (Inherited from CacheDependency)
ToString()	Returns a string that represents the current object. (Inherited from Object)