Recipe 3.7. Requiring Data to Match a Database Entry


Problem

You need to make sure the data a user enters matches an entry in a database.

Solution

Add a CustomValidator to the .aspx file. Then add an event handler to the codebehind for the CustomValidator control's ServerValidate event, its purpose beingto validate the user entries against the database.

In the .aspx file:

  1. Add a CustomValidator control that validates the entries against the database during server-side validation.

  2. Add a Login (or equivalently named) button.

In the code-behind class for the page, use the .NET language of your choice to:

  1. Add an event handler for the CustomValidator control's ServerValidate event, its purpose beingto provide the server-side validation of the user's entries against the database.

  2. Add code to the event handler for the Login button's click event to check the Page.IsValid property and verify that all validation was successful (see Recipe 3.1 for details).

Figure 3-12 shows a typical form with normal output prior to data entry. Figure 3-13 shows the form with a validation error message. Examples 3-10, 3-11 through 3-12 show the .aspx and code-behind files for our application that implements the solution.

Discussion

One of the most common examples of this recipe's handiness is when implementing a classic login page. The approach we favor in this scenario uses a CustomValidator to perform the user authentication and a ValidationSummary to display error information.

Figure 3-12. Form with database validation outputnormal


Figure 3-13. Form with database validation outputwith error message


In our example, RequiredFieldValidator controls are used for the login ID and password fields. (RequiredFieldValidator controls are described in Recipe 3.1.) The user must supply both to gain access to her account.

Unlike the other recipes in this chapter, our approach for this recipe has the CustomValidator control's EnableClientScript attribute set to False to disable client side validation because the database validation can be done only on the server side:

 <asp:CustomValidator  Runat="server"  Display="None"  EnableClientScript="False"  ErrorMessage="Login ID or Password Is Invalid"  OnServerValidate="cvAuthentication_ServerValidate" /> 

The ValidationSummary is set up to display all validation errors. This includes errors from the RequiredFieldValidator controls and the CustomValidator used for user authentication.

The ServerValidate event for the CustomValidator (cvAuthentication_ServerValidate) is used to perform the user authentication by checkingif a user exists in the database with the entered login ID and password, as shown in Examples 3-11 (VB) and 3-12 (C#).

If the user is found in the database, the args.IsValid property is set true to indicate the validation was successful. Otherwise, it is set False to indicate the validation failed.

The event handler for the Login button's click event (btnLogin_Click) then checks to see if the page is valid before proceeding with actions required to log the user into the system.

As you may have noticed, the approach used in this recipe is an amalgam of all the approaches used in the chapter's other recipes. Having used this approach to control essentially all the aspects of validation, you can adapt it to perform almost any validation your application requires.

See Also

Recipes 3.1 and 3.5

Example 3-10. Form with database validation (.aspx)

 <%@ Page Language="VB" MasterPageFile="~/ASPNetCookbookVB.master"  AutoEventWireup="false"  CodeFile="CH03CustomDatabaseValidationVB.aspx.vb"  Inherits="ASPNetCookbook.VBExamples.CH03CustomDatabaseValidationVB"  title="Custom Database Validation" %> <asp:Content  Runat="server" ContentPlaceHolder>    <div align="center" >  Custom Selection Validation (VB)    </div>    <table align="center" >   </tr>  <td colspan="2" align="left">     <asp:ValidationSummary  Runat="server" Css DisplayMode="BulletList" EnableClientScript="True" HeaderText="Error Summary" /> <asp:CustomValidator  Runat="server"   Display="None"   EnableClientScript="False"   ErrorMessage="Login ID or Password Is Invalid"   OnServerValidate="cvAuthentication_ServerValidate" />  </td>   </tr>   </tr>  <td >Login ID: </td>  <td> <asp:TextBox  Runat="server"  Columns="30" Css /> <asp:RequiredFieldValidator     Runat="server"    ControlToValidate="txtLoginID"    Css    Display="Dynamic"    EnableClientScript="True"    ErrorMessage="Login ID Is Required"> <img src="/books/1/505/1/html/2/images/arrow_alert.gif" alt="arrow"/> </asp:RequiredFieldValidator>  </td>   </tr>   </tr>      <td >Password: </td>  <td> <asp:TextBox  Runat="server" TextMode="Password" Columns="30" Css /> <asp:RequiredFieldValidator     Runat="server"    ControlToValidate="txtPassword"    Css    Display="Dynamic"    EnableClientScript="True"    ErrorMessage="Password Is Required">  <img src="/books/1/505/1/html/2/images/arrow_alert.gif" alt="arrow"/> </asp:RequiredFieldValidator>    </td> </tr> </tr>    <td colspan="2" align="center">   <br/>   <input  runat="server" type="button" value="Login" causesvalidation="true" onserverclick="btnLogin_Click"/>   </td>   </tr>    </table> </asp:Content> 

Example 3-11. Form with database validation code-behind (.vb)

 Option Explicit On Option Strict On Imports System.Configuration.ConfigurationManager Imports System.Data Imports System.Data.OleDb Namespace ASPNetCookbook.VBExamples   ''' <summary>   ''' This class provides the code behind for   ''' CH03CustomDatabaseValidationVB.aspx   ''' </summary>   Partial Class CH03CustomDatabaseValidationVB Inherits System.Web.UI.Page '''*********************************************************************** ''' <summary> ''' This routine provides the event handler for the authentication server ''' validate event. It is responsible for checking the login ID and ''' password in the database to authenticate the user. ''' </summary> ''' ''' <param name="source">Set to the sender of the event</param> ''' <param name="args">Set to the event arguments</param> Protected Sub cvAuthentication_ServerValidate(ByVal source As Object, _ ByVal args As ServerValidateEventArgs)    Dim dbConn As OleDbConnection = Nothing    Dim dCmd As OleDbCommand = Nothing    Dim strConnection As String    Dim strSQL As String    Try  'initially assume credentials are invalid  args.IsValid = False  'get the connection string from web.config and open a connection  'to the database  strConnection = _ ConnectionStrings("dbConnectionString").ConnectionString  dbConn = New OleDb.OleDbConnection(strConnection)  dbConn.Open( )  'build the query string and check to see if a user with the entered  'credentials exists in the database  strSQL = "SELECT AppUserID FROM AppUser " & _  "WHERE LoginID=? AND " & _  "Password=?"  dCmd = New OleDbCommand(strSQL, dbConn)  dCmd.Parameters.Add(New OleDbParameter("LoginID", _ txtLoginID.Text))  dCmd.Parameters.Add(New OleDbParameter("Password", _ txtPassword.Text))  'check to see if the user was found  If (Not IsNothing(dCmd.ExecuteScalar( ))) Then   args.IsValid = True      End If    Finally  'cleanup  If (Not IsNothing(dbConn)) Then    dbConn.Close( )  End If     End Try    End Sub 'cvAuthentication_ServerValidate    '''***********************************************************************    ''' <summary>    ''' This routine provides the event handler for the login button click    ''' event. It is responsible for processing the form data.    ''' </summary>    '''    ''' <param name="sender">Set to the sender of the event</param>    ''' <param name="e">Set to the event arguments</param>    Protected Sub btnLogin_Click(ByVal sender As Object, _  ByVal e As System.EventArgs)  If (Page.IsValid) Then    'user has been authenticated so proceed with allowing access    'to the site  End If  End Sub 'btnLogin_Click   End Class 'CH03CustomDatabaseValidationVB End Namespace 

Example 3-12. Form with database validation code-behind (.cs)

 using System; using System.Configuration; using System.Data; using System.Data.OleDb; namespace ASPNetCookbook.CSExamples {   /// <summary>   /// This class provides the code behind for   /// CH03CustomDatabaseValidationCS.aspx   /// </summary>   public partial class CH03CustomDatabaseValidationCS : System.Web.UI.Page   { ///***********************************************************************     /// <summary> /// This routine provides the event handler for the authentication server /// validate event. It is responsible checking the login ID and password /// in the database to authenticate the user. /// </summary> /// <param name="sender">Set to the sender of the event</param> /// <param name="e">Set to the event arguments</param> protected void cvAuthentication_ServerValidate(Object source, System.Web.UI.WebControls.ServerValidateEventArgs args) {    OleDbConnection dbConn = null;    OleDbCommand dCmd = null;    String strConnection = null;    String strSQL = null;    try    {     // initially assume credentials are invalid  args.IsValid = false;  // get the connection string from web.config and open a connection      // to the database  strConnection = ConfigurationManager.  ConnectionStrings["dbConnectionString"].ConnectionString;  dbConn = new OleDbConnection(strConnection);  dbConn.Open( );  // build the query string and check to see if a user with the  // entered credentials exists in the database  strSQL = "SELECT AppUserID FROM AppUser " + "WHERE LoginID=? AND " + "Password=?";  dCmd = new OleDbCommand(strSQL, dbConn);  dCmd.Parameters.Add(new OleDbParameter("LoginID", txtLoginID.Text));  dCmd.Parameters.Add(new OleDbParameter("Password", txtPassword.Text));  // check to see if the user was found  if (dCmd.ExecuteScalar( ) != null)  { args.IsValid = true;  }    } // try    finally    {  // cleanup  if (dbConn != null)  {    dbConn.Close( );  }    } // finally  } // cvAuthentication_ServerValidate  ///***********************************************************************  /// <summary>  /// This routine provides the event handler for the login button click  /// event. It is responsible for processing the form data.  /// </summary>  /// <param name="sender">Set to the sender of the event</param>  /// <param name="e">Set to the event arguments</param>  protected void btnLogin_Click(Object sender,   System.EventArgs e) {   if (Page.IsValid)   { // user has been authenticated so proceed with allowing access // to the site   } } //btnLogin_Click   } // CH03CustomDatabaseValidationCS } 



ASP. NET Cookbook
ASP.Net 2.0 Cookbook (Cookbooks (OReilly))
ISBN: 0596100647
EAN: 2147483647
Year: 2003
Pages: 202

Similar book on Amazon

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net