RequiredAttribute Class

Definition

public ref class RequiredAttribute : System::ComponentModel::DataAnnotations::ValidationAttribute

[System.AttributeUsage(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]public class RequiredAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute

[System.AttributeUsage(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false)]public class RequiredAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute

[<System.AttributeUsage(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)>]type RequiredAttribute = class    inherit ValidationAttribute

[<System.AttributeUsage(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false)>]type RequiredAttribute = class    inherit ValidationAttribute

Public Class RequiredAttributeInherits ValidationAttribute

Inheritance

Object

Attribute

ValidationAttribute

RequiredAttribute

Attributes

AttributeUsageAttribute

Examples

The following example uses theRequiredAttribute 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 theRequiredAttribute 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;}

Imports System.Web.DynamicDataImports System.ComponentModel.DataAnnotationsImports System.Globalization<MetadataType(GetType(CustomerMetaData))> _Partial Public Class Customer   End ClassPublic Class CustomerMetaData    ' Require that the Title is not null.    ' Use custom validation error.    <Required(ErrorMessage:="Title is required.")> _    Public Title As Object    ' Require that the MiddleName is not null.    ' Use standard validation error.    <Required()> _    Public MiddleName As ObjectEnd Class

Remarks

TheRequiredAttribute 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 isnull, contains an empty string (""), or contains only white-space characters.