RequiredAttribute Class

Definition

Namespace:

System.ComponentModel.DataAnnotations

Assembly:

System.ComponentModel.Annotations.dll

Source:

RequiredAttribute.cs

Specifies that a data field value is required.

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.Parameter | System.AttributeTargets.Property, AllowMultiple=false)>]
type RequiredAttribute = class
    inherit ValidationAttribute

Public Class RequiredAttribute
Inherits ValidationAttribute

Inheritance

Object

Attribute

ValidationAttribute

RequiredAttribute

Attributes

AttributeUsageAttribute

Examples

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;
}

Imports System.Web.DynamicData
Imports System.ComponentModel.DataAnnotations
Imports System.Globalization

<MetadataType(GetType(CustomerMetaData))> _
Partial Public Class Customer

   
End Class

Public 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 Object

End Class

Remarks

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.

Constructors

RequiredAttribute()

Initializes a new instance of the RequiredAttribute class.

Properties

AllowEmptyStrings	Gets or sets a value that indicates whether an empty string is allowed.
ErrorMessage	Gets or sets an error message to associate with a validation control if validation fails. (Inherited from ValidationAttribute)
ErrorMessageResourceName	Gets or sets the error message resource name to use in order to look up the ErrorMessageResourceType property value if validation fails. (Inherited from ValidationAttribute)
ErrorMessageResourceType	Gets or sets the resource type to use for error-message lookup if validation fails. (Inherited from ValidationAttribute)
ErrorMessageString	Gets the localized validation error message. (Inherited from ValidationAttribute)
RequiresValidationContext	Gets a value that indicates whether the attribute requires validation context. (Inherited from ValidationAttribute)
TypeId	When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute)
FormatErrorMessage(String)	Applies formatting to an error message, based on the data field where the error occurred. (Inherited from ValidationAttribute)
GetHashCode()	Returns the hash code for this instance. (Inherited from Attribute)
GetType()	Gets the Type of the current instance. (Inherited from Object)
GetValidationResult(Object, ValidationContext)	Checks whether the specified value is valid with respect to the current validation attribute. (Inherited from ValidationAttribute)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute)
IsValid(Object)	Checks that the value of the required data field is not empty.
IsValid(Object, ValidationContext)	Validates the specified value with respect to the current validation attribute. (Inherited from ValidationAttribute)
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)
Validate(Object, String)	Validates the specified object. (Inherited from ValidationAttribute)
Validate(Object, ValidationContext)	Validates the specified object. (Inherited from ValidationAttribute)