ObjectDataSource.CacheKeyDependency Property
Definition
Important
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Gets or sets a user-defined key dependency that is linked to all data cache objects that are created by the data source control.
public:
virtual property System::String ^ CacheKeyDependency { System::String ^ get(); void set(System::String ^ value); };public virtual string CacheKeyDependency { get; set; }member this.CacheKeyDependency : string with get, setPublic Overridable Property CacheKeyDependency As StringProperty Value
A key that identifies all cache objects created by the ObjectDataSource.
Examples
The following three examples show a Web page, a code-behind page class, and a data-access class that retrieve records from the Employees table in the Northwind database.
The first example shows a Web page that contains two ObjectDataSource controls, a DropDownList control, and a DetailsView control. The first ObjectDataSource control and the DropDownList control are used to retrieve and display employee names from the database. The second ObjectDataSource control and the DetailsView control are used to retrieve and display the employee record that is selected by the user.
Caching is enabled for the ObjectDataSource control. Therefore, each record is retrieved only one time from the database. The CacheKeyDependency property is set to "EmployeeDetails", but any string value can work as the key. The Web page also includes a Button control that the user can click to expire the cached data.
<form id="form1" runat="server">
<div>
<asp:objectdatasource
ID="ObjectDataSource1"
runat="server"
SelectMethod="GetFullNamesAndIDs"
TypeName="Samples.AspNet.CS.EmployeeLogic" />
<p>
<asp:dropdownlist
ID="DropDownList1"
runat="server"
DataSourceID="ObjectDataSource1"
DataTextField="FullName"
DataValueField="EmployeeID"
AutoPostBack="True"
AppendDataBoundItems="true">
<asp:ListItem Text="Select One" Value=""></asp:ListItem>
</asp:dropdownlist>
</p>
<asp:objectdatasource
ID="ObjectDataSource2"
runat="server"
SelectMethod="GetEmployee"
TypeName="Samples.AspNet.CS.EmployeeLogic"
EnableCaching="true"
CacheKeyDependency="EmployeeDetails" >
<SelectParameters>
<asp:ControlParameter ControlID="DropDownList1" DefaultValue="-1" Name="empID" />
</SelectParameters>
</asp:objectdatasource>
<asp:DetailsView
ID="DetailsView1"
runat="server"
DataSourceID="ObjectDataSource2"
AutoGenerateRows="false">
<Fields>
<asp:BoundField HeaderText="Address" DataField="Address" />
<asp:BoundField HeaderText="City" DataField="City" />
<asp:BoundField HeaderText="Postal Code" DataField="PostalCode" />
</Fields>
</asp:DetailsView>
<asp:Button
ID="Button1"
runat="server"
Text="Check for latest data"
OnClick="Button1_Click" />
</div>
</form>
<form id="form1" runat="server">
<div>
<asp:objectdatasource
ID="ObjectDataSource1"
runat="server"
SelectMethod="GetFullNamesAndIDs"
TypeName="Samples.AspNet.CS.EmployeeLogic" />
<p>
<asp:dropdownlist
ID="DropDownList1"
runat="server"
DataSourceID="ObjectDataSource1"
DataTextField="FullName"
DataValueField="EmployeeID"
AutoPostBack="True"
AppendDataBoundItems="true">
<asp:ListItem Text="Select One" Value=""></asp:ListItem>
</asp:dropdownlist>
</p>
<asp:objectdatasource
ID="ObjectDataSource2"
runat="server"
SelectMethod="GetEmployee"
TypeName="Samples.AspNet.CS.EmployeeLogic"
EnableCaching="true"
CacheKeyDependency="EmployeeDetails" >
<SelectParameters>
<asp:ControlParameter ControlID="DropDownList1" DefaultValue="-1" Name="empID" />
</SelectParameters>
</asp:objectdatasource>
<asp:DetailsView
ID="DetailsView1"
runat="server"
DataSourceID="ObjectDataSource2"
AutoGenerateRows="false">
<Fields>
<asp:BoundField HeaderText="Address" DataField="Address" />
<asp:BoundField HeaderText="City" DataField="City" />
<asp:BoundField HeaderText="Postal Code" DataField="PostalCode" />
</Fields>
</asp:DetailsView>
<asp:Button
ID="Button1"
runat="server"
Text="Check for latest data"
OnClick="Button1_Click" />
</div>
</form>
The second example shows a handler for the Load event and a handler for the Click event of the Button control. The Load event handler creates a cache item with a key set to the CacheKeyDependency value. The Click event handler removes the cache item whose key is equal to the CacheKeyDependency value. When the cache item is removed, all the cached data that is dependent on the key is expired.
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Cache[ObjectDataSource2.CacheKeyDependency] = "CacheExample";
}
}
protected void Button1_Click(object sender, EventArgs e)
{
Cache.Remove(ObjectDataSource2.CacheKeyDependency);
Cache[ObjectDataSource2.CacheKeyDependency] = "CacheExample";
DetailsView1.DataBind();
}
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
If Not (IsPostBack) Then
Cache(ObjectDataSource2.CacheKeyDependency) = "CacheExample"
End If
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)
Cache.Remove(ObjectDataSource2.CacheKeyDependency)
Cache(ObjectDataSource2.CacheKeyDependency) = "CacheExample"
DetailsView1.DataBind()
End Sub
The third example shows the data access class that interacts with the Northwind database. The class uses LINQ to query the Employees table. The example requires a LINQ to SQL class that represents the Northwind database and the Employees table. For more information, see How to: Create LINQ to SQL Classes in a Web Project.
public class EmployeeLogic
{
public static Array GetFullNamesAndIDs()
{
NorthwindDataContext ndc = new NorthwindDataContext();
var employeeQuery =
from e in ndc.Employees
orderby e.LastName
select new { FullName = e.FirstName + " " + e.LastName, EmployeeID = e.EmployeeID };
return employeeQuery.ToArray();
}
public static Employee GetEmployee(int empID)
{
if (empID < 0)
{
return null;
}
else
{
NorthwindDataContext ndc = new NorthwindDataContext();
var employeeQuery =
from e in ndc.Employees
where e.EmployeeID == empID
select e;
return employeeQuery.Single();
}
}
public static void UpdateEmployeeAddress(Employee originalEmployee, string address, string city, string postalcode)
{
NorthwindDataContext ndc = new NorthwindDataContext();
ndc.Employees.Attach(originalEmployee, false);
originalEmployee.Address = address;
originalEmployee.City = city;
originalEmployee.PostalCode = postalcode;
ndc.SubmitChanges();
}
}
Public Class EmployeeLogic
Public Shared Function GetFullNamesAndIDs() As Array
Dim ndc As New NorthwindDataContext()
Dim employeeQuery = _
From e In ndc.Employees _
Order By e.LastName _
Select FullName = e.FirstName + " " + e.LastName, EmployeeID = e.EmployeeID
Return employeeQuery.ToArray()
End Function
Public Shared Function GetEmployee(ByVal empID As Integer) As Employee
If (empID < 0) Then
Return Nothing
Else
Dim ndc As New NorthwindDataContext()
Dim employeeQuery = _
From e In ndc.Employees _
Where e.EmployeeID = empID _
Select e
Return employeeQuery.Single()
End If
End Function
Public Shared Sub UpdateEmployeeAddress(ByVal originalEmployee As Employee, ByVal address As String, ByVal city As String, ByVal postalcode As String)
Dim ndc As New NorthwindDataContext()
ndc.Employees.Attach(originalEmployee, False)
originalEmployee.Address = address
originalEmployee.City = city
originalEmployee.PostalCode = postalcode
ndc.SubmitChanges()
End Sub
End Class
Remarks
The CacheKeyDependency property can be set to any arbitrary string value.
All cache objects are explicitly expired when the key is expired. This allows you to invalidate cache entries that are created by the ObjectDataSource from your own page code programmatically.
The ObjectDataSource control supports data caching. While data is cached, calls to the Select method retrieve data from the cache rather than from the business object that the ObjectDataSource works with. When the cache expires, the Select method retrieves data from the business object, and then caches the data again.
The ObjectDataSource control automatically caches data when the EnableCaching property is set to true and the CacheDuration property is set to a value greater than 0, which indicates the number of seconds that the cache stores data before the cache entry is discarded. A value of 0 indicates an infinitely long cache.
You can set the CacheKeyDependency property to create a dependency between all cache entries that are created by the ObjectDataSource control and the key. You can expire all the cache entries programmatically at any time by expiring the key. Expire the key by using the Cache.Remove method with the current CacheKeyDependency value as the parameter.
A unique cache entry is created for every combination of the CacheDuration, CacheExpirationPolicy, TypeName, SelectMethod, and SelectParameters properties. Multiple ObjectDataSource controls can use the same cache entries in scenarios where they load data using the same type, method, and parameters.
