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RequiredAttribute Class

Specifies that a data field value is required.

System.Object
  System.Attribute
    System.ComponentModel.DataAnnotations.ValidationAttribute
      System.ComponentModel.DataAnnotations.RequiredAttribute

Namespace:  System.ComponentModel.DataAnnotations
Assembly:  System.ComponentModel.DataAnnotations (in System.ComponentModel.DataAnnotations.dll)

[AttributeUsageAttribute(AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Parameter, AllowMultiple = false)]
public class RequiredAttribute : ValidationAttribute

The RequiredAttribute type exposes the following members.

  NameDescription
Public methodRequiredAttributeInitializes a new instance of the RequiredAttribute class.
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  NameDescription
Public propertyAllowEmptyStringsGets or sets a value that indicates whether an empty string is allowed.
Public propertyErrorMessageGets or sets an error message to associate with a validation control if validation fails. (Inherited from ValidationAttribute.)
Public propertyErrorMessageResourceNameGets or sets the error message resource name to use in order to look up the ErrorMessageResourceType property value if validation fails. (Inherited from ValidationAttribute.)
Public propertyErrorMessageResourceTypeGets or sets the resource type to use for error-message lookup if validation fails. (Inherited from ValidationAttribute.)
Protected propertyErrorMessageStringGets the localized validation error message. (Inherited from ValidationAttribute.)
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodFormatErrorMessageApplies formatting to an error message, based on the data field where the error occurred. (Inherited from ValidationAttribute.)
Public methodGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetValidationResultChecks whether the specified value is valid with respect to the current validation attribute. (Inherited from ValidationAttribute.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodIsValid(Object)Checks that the value of the required data field is not empty. (Overrides ValidationAttribute.IsValid(Object).)
Protected methodIsValid(Object, ValidationContext)Validates the specified value with respect to the current validation attribute. (Inherited from ValidationAttribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodValidate(Object, ValidationContext)Validates the specified object. (Inherited from ValidationAttribute.)
Public methodValidate(Object, String)Validates the specified object. (Inherited from ValidationAttribute.)
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  NameDescription
Explicit interface implemetationPrivate method_Attribute.GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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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.

NoteNote

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

Supported in: 4, 3.5 SP1

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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