RequiredAttribute Class

The RequiredAttribute attribute specifies that when a field on a form is validated, the field must contain a value. A validation exception is raised if the property is null, contains an empty string (""), or contains only white-space characters.

Note
If the MVC data model or entity partial class contains a field that is annotated with the RequiredAttribute attribute, but the page does not contain the property, an error is not raised. Validation occurs only for fields that are submitted to the server.

A Visual Studio project with source code is available to accompany this topic: Download.

The following example uses the RequiredAttribute attribute to override the database schema rule that allows a data field to be empty. The example performs the following steps:

• Implements a metadata partial class and the associated metadata class.

• In the associated metadata class, it applies the RequiredAttribute attribute, which specifies the following requirements:

  • The Title data field cannot be empty. If validation fails, the code in the example throws a validation exception and displays an error message. The error message is specified at the time that the attribute is applied to the data field.

  • The MiddleName data field cannot be empty. If validation fails, the code in the example throws a validation exception and displays an error message.

using System;
using System.Web.DynamicData;
using System.ComponentModel.DataAnnotations;
using System.Globalization;

[MetadataType(typeof(CustomerMetaData))]
public partial class Customer
{


}

public class CustomerMetaData
{
    // Require that the Title is not null.
    // Use custom validation error.
    [Required(ErrorMessage = "Title is required.")]
    public object Title;

    // Require that the MiddleName is not null.
    // Use standard validation error.
    [Required()]
    public object MiddleName;

}

.NET Framework

.NET Framework Client Profile

Windows 8 Consumer Preview, Windows Server 8 Beta, Windows 7, Windows Server 2008 SP2, Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference