ObjectDataSource.SelectCountMethod Property
Definition
Important
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Gets or sets the name of the method or function that the ObjectDataSource control invokes to retrieve a row count.
public:
property System::String ^ SelectCountMethod { System::String ^ get(); void set(System::String ^ value); };public string SelectCountMethod { get; set; }member this.SelectCountMethod : string with get, setPublic Property SelectCountMethod As StringProperty Value
A string that represents the name of the method or function that the ObjectDataSource uses to retrieve a row count. The method must return an integer (Int32). The default is an empty string ("").
Examples
The following three examples show a Web page, a code-behind page class, and a data-access class that enable the user to pick how many records are displayed in the page.
The Web page contains an ObjectDataSource control whose EnablePaging property is set to true. The SelectCountMethod property is set to the name of a method that returns the total number of records in the query. The MaximumRowsParameterName property and the StartRowIndexParameterName property are set to the names of the parameters that are used in the Select method. The page also contains a DropDownList control.
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>ObjectDataSource Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
How many rows to display on this page:<br />
<asp:DropDownList
AutoPostBack="true"
ID="rowsToDisplay"
runat="server"
onselectedindexchanged="rowsToDisplay_SelectedIndexChanged">
<asp:ListItem Value="5"></asp:ListItem>
<asp:ListItem Value="10" Selected="True"></asp:ListItem>
<asp:ListItem Value="20"></asp:ListItem>
</asp:DropDownList>
<asp:ObjectDataSource
SelectCountMethod="GetEmployeeCount"
EnablePaging="true"
TypeName="CustomerLogic"
SelectMethod="GetSubsetOfEmployees"
MaximumRowsParameterName="maxRows"
StartRowIndexParameterName="startRows"
ID="ObjectDataSource1"
runat="server">
</asp:ObjectDataSource>
<asp:GridView
DataSourceID="ObjectDataSource1"
AllowPaging="true"
ID="GridView1"
runat="server">
</asp:GridView>
</div>
</form>
</body>
</html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
How many rows to display on this page:<br />
<asp:DropDownList
AutoPostBack="true"
ID="rowsToDisplay"
runat="server"
onselectedindexchanged="rowsToDisplay_SelectedIndexChanged">
<asp:ListItem Value="5"></asp:ListItem>
<asp:ListItem Value="10" Selected="True"></asp:ListItem>
<asp:ListItem Value="20"></asp:ListItem>
</asp:DropDownList>
<asp:ObjectDataSource
SelectCountMethod="GetEmployeeCount"
EnablePaging="true"
TypeName="CustomerLogic"
SelectMethod="GetSubsetOfEmployees"
MaximumRowsParameterName="maxRows"
StartRowIndexParameterName="startRows"
ID="ObjectDataSource1"
runat="server">
</asp:ObjectDataSource>
<asp:GridView
DataSourceID="ObjectDataSource1"
AllowPaging="true"
ID="GridView1"
runat="server">
</asp:GridView>
</div>
</form>
</body>
</html>
The second example shows a handler for the ListControl.SelectedIndexChanged event of the DropDownList control. The code in the handler sets the PageSize property to the user's selection.
protected void rowsToDisplay_SelectedIndexChanged(object sender, EventArgs e)
{
GridView1.PageSize = int.Parse(rowsToDisplay.SelectedValue);
}
Protected Sub rowsToDisplay_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles rowsToDisplay.SelectedIndexChanged
GridView1.PageSize = Integer.Parse(rowsToDisplay.SelectedValue)
End Sub
The third example shows the data access class that retrieves data from the Customers table. It includes a method named GetSubsetOfEmployees, which is assigned to the SelectMethod property of the ObjectDataSource control. The example also includes a method named GetEmployeeCount, which is assigned to the SelectCountMethod property of the ObjectDataSource control. The class uses LINQ to query the Customers table. The example requires a LINQ to SQL class that represents the Northwind database and Customers table. For more information, see How to: Create LINQ to SQL Classes in a Web Project.
public class CustomerLogic
{
public List<Customer> GetSubsetOfEmployees(int startRows, int maxRows)
{
NorthwindDataContext ndc = new NorthwindDataContext();
var customerQuery =
from c in ndc.Customers
select c;
return customerQuery.Skip(startRows).Take(maxRows).ToList<Customer>();
}
public int GetEmployeeCount()
{
object cachedCount = HttpRuntime.Cache["TotalEmployeeCount"];
if (cachedCount != null)
{
return int.Parse(cachedCount.ToString());
}
else
{
NorthwindDataContext ndc = new NorthwindDataContext();
var totalNumberQuery =
from c in ndc.Customers
select c;
int employeeCount = totalNumberQuery.Count();
HttpRuntime.Cache.Add("TotalEmployeeCount", employeeCount, null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null);
return employeeCount;
}
}
}
Public Class CustomerLogic
Public Function GetSubsetOfEmployees(ByVal startRows As Integer, ByVal maxRows As Integer) As List(Of Customer)
Dim ndc As New NorthwindDataContext()
Dim customerQuery = _
From c In ndc.Customers _
Select c
Return customerQuery.Skip(startRows).Take(maxRows).ToList()
End Function
Public Function GetEmployeeCount() As Integer
Dim cachedCount = HttpRuntime.Cache("TotalEmployeeCount")
If cachedCount IsNot Nothing Then
Return Integer.Parse(cachedCount.ToString())
Else
Dim ndc As New NorthwindDataContext()
Dim totalNumberQuery = _
From c In ndc.Customers _
Select c
Dim employeeCount = totalNumberQuery.Count()
HttpRuntime.Cache.Add("TotalEmployeeCount", employeeCount, Nothing, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.Normal, Nothing)
Return employeeCount
End If
End Function
End Class
Remarks
The SelectCountMethod property identifies a business object method that is used to retrieve a total row count, to support data source paging. The SelectCountMethod property is evaluated only if the EnablePaging property is set to true.
The SelectCountMethod property delegates to the SelectCountMethod property of the ObjectDataSourceView object that is associated with the ObjectDataSource control. For information about how paging is supported by the ObjectDataSource control, see EnablePaging.
