FilterExpression Property

ObjectDataSourceView.FilterExpression Property

 

Gets or sets a filtering expression that is applied when the business object method that is identified by the SelectMethod property is called.

Namespace:   System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

Public Property FilterExpression As String

Property Value

Type: System.String

A string that represents a filtering expression applied when data is retrieved using the business object method identified by the SelectMethod property.

Exception Condition
NotSupportedException

The FilterExpression property was set and the Select method does not return a DataSet.

The ObjectDataSource control supports filtering data only when the Select method returns a DataSet, DataView, or DataTable object.

The syntax that is used for the FilterExpression property is a format string-style expression. The filter expression syntax is the same syntax that is accepted by the RowFilter property because the filter expression is applied to the RowFilter property of the DataView object that is returned from executing the Select method. (For more information, see Expression.) If you add parameters to the FilterParameters collection, you can also include format string placeholders, for example "{0}", in the expression to substitute for parameter values. The placeholders are replaced according to the index of the parameter in the FilterParameters collection.

You can include parameters in the FilterExpression. If the type of the parameter is a string or character type, enclose the parameter in single quotation marks. Quotation marks are not needed if the parameter is a numeric type.The FilterParameters collection contains the parameters that are evaluated for the placeholders found in the FilterExpression.

The value of the FilterExpression property is stored in view state.

System_CAPS_security Security Note

It is recommended that you validate any filter parameter value that you receive from the client. The runtime simply substitutes the parameter value into the filter expression and applies it to the DataView object that is returned by the Select method. If you are using the FilterExpression property as a security measure to limit the number of items that are returned, you must validate the parameter values before the filtering occurs.

This section contains two code examples. The first code example demonstrates how to display filtered data using an ObjectDataSource control to retrieve data from a middle-tier business object and a GridView control to display the results. The second code example provides an example of the middle-tier business object that is used in the first code example.

The following code example demonstrates how to display filtered data using an ObjectDataSource control to retrieve data from a middle-tier business object and a GridView control to display the results. The ObjectDataSource control can filter data only when the method that retrieves the data retrieves it as a DataSet object. For this reason, the SelectMethod property identifies a business object method that retrieves data as a DataSet.

The code example consists of a TextBox, a GridView control, the ObjectDataSource control, and a Submit button. By default, the TextBox is populated with the name of one of the Northwind Traders employees. The GridView displays information about the employee that is identified by the name in the TextBox. To retrieve data on another employee, in the TextBox, enter the full name of the employee, and then click the Submit button.

The FilterExpression property specifies an expression that is used to filter the data that is retrieved by the SelectMethod property. It uses parameter placeholders that are evaluated to the parameters that are contained in the FilterParameters collection. In this example, the parameter placeholder is bounded by single quotation marks because the type of the parameter is a string type that might contain spaces. If the type of the parameter is a numeric or date type, bounding quotation marks are not required.

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB" Assembly="Samples.AspNet.VB" %>
<%@ Page language="vb" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">

    Protected Sub ObjectDataSource1_Filtering(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ObjectDataSourceFilteringEventArgs)
        If Textbox1.Text = "" Then
            e.ParameterValues.Clear()
            e.ParameterValues.Add("FullName", "Nancy Davolio")
        End If
    End Sub
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>ObjectDataSource - VB Example</title>
  </head>
  <body>
    <form id="Form1" method="post" runat="server">

        <p>Show all users with the following name.</p>

        <asp:textbox id="Textbox1" runat="server" text="Nancy Davolio" />

        <asp:gridview
          id="GridView1"
          runat="server"
          datasourceid="ObjectDataSource1"
          autogeneratecolumns="False">
          <columns>
            <asp:boundfield headertext="ID" datafield="EmpID" />
            <asp:boundfield headertext="Name" datafield="FullName" />
            <asp:boundfield headertext="Street Address" datafield="Address" />
          </columns>
        </asp:gridview>

        <!-- Security Note: The ObjectDataSource uses a FormParameter,
             Security Note: which does not perform validation of input from the client. -->

        <asp:objectdatasource
          id="ObjectDataSource1"
          runat="server"
          selectmethod="GetAllEmployeesAsDataSet"
          typename="Samples.AspNet.VB.EmployeeLogic"
          filterexpression="FullName='{0}'" OnFiltering="ObjectDataSource1_Filtering">
            <filterparameters>
              <asp:formparameter name="FullName" formfield="Textbox1" defaultvalue="Nancy Davolio" />
            </filterparameters>
        </asp:objectdatasource>

        <p><asp:button id="Button1" runat="server" text="Search" /></p>

    </form>
  </body>
</html>

The following code example provides an example of a middle-tier business object that the preceding code example uses. The code example consists of two basic classes:

  • The EmployeeLogic class, which is a class that encapsulates business logic.

  • The NorthwindEmployee class, which is a model class that contains only the basic functionality that is required to load and persist data from the data tier.

For simplicity, the EmployeeLogic class creates a static set of data, rather than retrieving the data from a data tier. It is also helpful for this example, because the sample relies on you to provide the full name of a Northwind Traders employee to demonstrate filtering.

For a complete working example, you must compile and use these classes with the Web Forms page code examples that are provided.

Imports System
Imports System.Collections
Imports System.Data
Imports System.Web.UI.WebControls

Namespace Samples.AspNet.VB
'
' EmployeeLogic is a stateless business object that encapsulates 
' the operations you can perform on a NorthwindEmployee object.
'
Public Class EmployeeLogic

   ' Returns a collection of NorthwindEmployee objects.
   Public Shared Function GetAllEmployees() As ICollection
      Dim data As New ArrayList()

      data.Add(New NorthwindEmployee(1, "Nancy", "Davolio", "507 - 20th Ave. E. Apt. 2A"))
      data.Add(New NorthwindEmployee(2, "Andrew", "Fuller", "908 W. Capital Way"))
      data.Add(New NorthwindEmployee(3, "Janet", "Leverling", "722 Moss Bay Blvd."))
      data.Add(New NorthwindEmployee(4, "Margaret", "Peacock", "4110 Old Redmond Rd."))
      data.Add(New NorthwindEmployee(5, "Steven", "Buchanan", "14 Garrett Hill"))
      data.Add(New NorthwindEmployee(6, "Michael", "Suyama", "Coventry House Miner Rd."))
      data.Add(New NorthwindEmployee(7, "Robert", "King", "Edgeham Hollow Winchester Way"))

      Return data
   End Function 'GetAllEmployees


   Public Shared Function GetEmployee(anID As Object) As NorthwindEmployee
      Dim data As ArrayList = CType(GetAllEmployees(), ArrayList)
      Dim empID As Integer = Int32.Parse(anID.ToString())
      Return CType(data(empID),NorthwindEmployee)   
   End Function 'GetEmployee


   ' To support basic filtering, the employees cannot
   ' be returned as an array of objects, rather as a 
   ' DataSet of the raw data values. 
   Public Shared Function GetAllEmployeesAsDataSet() As DataSet
      Dim employees As ICollection = GetAllEmployees()

      Dim ds As New DataSet("Table")

      ' Create the schema of the DataTable.
      Dim dt As New DataTable()
      Dim dc As DataColumn
      dc = New DataColumn("EmpID", GetType(Integer))
      dt.Columns.Add(dc)
      dc = New DataColumn("FullName", GetType(String))
      dt.Columns.Add(dc)
      dc = New DataColumn("Address", GetType(String))
      dt.Columns.Add(dc)

      ' Add rows to the DataTable.
      Dim row As DataRow
      Dim ne As NorthwindEmployee
      For Each ne In employees         
         row = dt.NewRow()
         row("EmpID") = ne.EmpID
         row("FullName") = ne.FullName
         row("Address") = ne.Address
         dt.Rows.Add(row)
      Next
      ' Add the complete DataTable to the DataSet.
      ds.Tables.Add(dt)

      Return ds
   End Function 'GetAllEmployeesAsDataSet

End Class 'EmployeeLogic 


Public Class NorthwindEmployee

   Public Sub New(anID As Integer, aFirstName As String, aLastName As String, anAddress As String)
      ID = anID
      Me.aFirstName = aFirstName
      Me.aLastName = aLastName
      Me.aAddress = anAddress
   End Sub 'NewNew

   Private ID As Object   
   Public ReadOnly Property EmpID() As String
      Get
         Return ID.ToString()
      End Get
   End Property 

   Private aLastName As String   
   Public Property LastName() As String
      Get
         Return aLastName
      End Get
      Set
         aLastName = value
      End Set
   End Property 

   Private aFirstName As String   
   Public Property FirstName() As String
      Get
         Return aFirstName
      End Get
      Set
         aFirstName = value
      End Set
   End Property 

   Public ReadOnly Property FullName() As String
      Get
         Return FirstName & " " & LastName
      End Get
   End Property 

   Private aAddress As String  
   Public Property Address() As String
      Get
         Return aAddress
      End Get
      Set
         aAddress = value
      End Set
   End Property 

End Class 'NorthwindEmployee
End Namespace

.NET Framework
Available since 2.0
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