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This chapter is from the book

This chapter is from the book

Creating a New Field Template

The set of field templates provided by Dynamic Data can be extended whenever a special data entry control is needed to handle values of a certain type. For example, the Northwind database uses regular string columns to store phone numbers for customers, employees, suppliers, and shippers. The phone numbers already stored in the database are in a consistent (###)###-#### format; however, Dynamic Data uses the regular Text_Edit field template for these columns, which does not enforce the phone number format. It would be nice to create a field template that would help users enter the phone numbers correctly.

You create a new field template by adding a new user control to the DynamicData\FieldTemplates folder of your project. You can also copy an existing field template that most closely matches the desired functionality. If you do copy an existing field template, remember to change the class name in both markup and code-behind files. In this example, however, we will start from scratch and create a new user control called PhoneNumber_Edit, shown in Listing 3.11.

Listing 3.11. PhoneNumber_Edit Field Template (Markup)

<%@ Control Language="C#" CodeBehind="PhoneNumber_Edit.ascx.cs"
  Inherits="WebApplication.DynamicData.FieldTemplates.PhoneNumberEditField" %>

<asp:TextBox ID="textBox" runat="server" Text='<%# FieldValueEditString %>'/>
<ajax:FilteredTextBoxExtender TargetControlID="textBox" runat="server"
  FilterType="Custom" ValidChars="+()-1234567890" />

<asp:RequiredFieldValidator runat="server" ID="requiredFieldValidator"
  ControlToValidate="textBox" Enabled="false" />
<asp:RegularExpressionValidator runat="server" ID="regularExpressionValidator"
  ControlToValidate="textBox" />
<asp:DynamicValidator runat="server" ID="dynamicValidator"
  ControlToValidate="textBox" />

As you can see, the PhoneNumber_Edit field template is similar to the DateTime template discussed earlier. It has a TextBox control used to enter the phone number, a FilteredTextBoxExtender, another AJAX control used to prevent users from entering symbols that would not be valid in a phone number, as well as several validator controls.

Although having a single DynamicValidator control is sufficient to enforce all validation attributes applied to the column in the data model, this control performs validation only on the server side, which requires a post-back before the error can be reported. Other ASP.NET validation controls, such as the RequiredFieldValidator, are optional, but because they also offer client-side validation logic, it’s best to include them in field templates to provide immediate feedback to the user, and improve the data entry experience.

Listing 3.12 shows the code-behind of the PhoneNumber_Edit field template.

Listing 3.12. PhoneNumber_Edit Field Template (Code-Behind)

using System;
using System.Collections.Specialized;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Web;
using System.Web.DynamicData;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication.DynamicData.FieldTemplates
  public partial class PhoneNumberEditField : FieldTemplateUserControl
    public override Control DataControl
      get { return this.textBox; }

    protected void Page_Load(object sender, EventArgs e)
      this.textBox.ToolTip = this.Column.Description;


    protected override void ExtractValues(IOrderedDictionary dictionary)
      dictionary[this.Column.Name] = this.ConvertEditedValue(this.textBox.Text);

    private void SetUpRegexValidator(RegularExpressionValidator validator)
      RegularExpressionAttribute attribute = this.Column.Attributes
      if (attribute == null)
        attribute = new RegularExpressionAttribute(@"\(\d{3}\)\d{3}-\d{4}");
        attribute.ErrorMessage = "The field {0} must be a valid phone number.";

      validator.Enabled = true;
      validator.Text = "*";
      validator.ValidationExpression = attribute.Pattern;
      validator.ErrorMessage = HttpUtility.HtmlEncode(
      validator.ToolTip = validator.ErrorMessage;


Most of the phone number validation in the new field template is performed by the standard ASP.NET control, RegularExpressionValidator, which ensures that the value entered by the user matches the regular expression pattern that defines a valid phone number. In addition to the server-side validation based on the .NET implementation of regular expressions in the System.Text.RegularExpressions namespace, it also works on the client side taking advantage of the regular expression functionality in JavaScript.

The RegularExpressionValidator is configured by the SetUpRegexValidator method defined in the code-behind. This method first searches the list of attributes applied to the column in the data model, Column.Attributes, for a RegularExpressionAttribute that might have been supplied by the application developer to indicate the expected phone number pattern. If no such attribute exists, this method creates a default Regular ExpressionAttribute with the pattern, \(\d{3}\)\d{3}-\d{4}, that matches U.S. phone numbers, such as (877)514-9180, with a three-digit area code in parentheses, followed by a seven-digit local number. The default attribute also has a generic error message that says that a column must be a valid phone number.

Having obtained the RegularExpressionAttribute instance, the SetUpRegexValidator method configures the RegularExpressionValidator control consistently with how the SetUpValidator method of the FieldTemplateUserControl base class does it—the Text displayed by the validator itself is always a star symbol; its ErrorMessage is reported through a ValidationSummary control on the page and the ToolTip contains the complete error message.

The last step in setting up the RegularExpressionValidator is to call the IgnoreModel ValidationAttribute method of the FieldTemplateUserControl base class. This allows the DynamicValidator to ignore the RegularExpressionAttribute during its validation because this attribute is already covered by the RegularExpressionValidator. Aside from helping to avoid doing the same validation check twice, this also prevents the regular expression validation error from being reported twice—first by the RegularExpression Validator and then by the DynamicValidator control.

Listing 3.13 shows an example of how the new PhoneNumber_Edit field template can be associated with a column using data annotation attributes.

Listing 3.13. Associating PhoneNumber Template with a Column

using System.ComponentModel.DataAnnotations;

namespace DataModel
  partial class Employee
    public class Metadata
      public object BirthDate;

      public object HireDate;

        ErrorMessage = "The Home Phone must be a valid phone number.")]
      public object HomePhone;

DataTypeAttribute, applied to the HomePhone column, specifies this string column’s actual data type is PhoneNumber. Dynamic Data uses this information as a hint when looking for a matching field template for this column and chooses the new PhoneNumber_Edit template instead of the default Text_Edit. In this example, RegularExpressionAttribute is also applied to the HomePhone column to provide a pattern that matches not only U.S. phone numbers, which have three-digit area codes, but also UK numbers, which might have two-digit area codes.

Figure 3.3 shows the Employee Edit page after the implementation of the PhoneNumber_Edit field template has been completed. Although you cannot tell from this screenshot, thanks to the FilteredTextBoxExtender, you cannot type any alphabetical symbols in the phone number text box. The pattern validation is performed on the client side as soon as you tab out of the text box, such as in this case, where one digit was removed from an otherwise valid UK phone number.

Figure 3.3

Figure 3.3. Employee Edit page with the New PhoneNumber_Edit field template.

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