RequiredAttribute Class

 

Specifies that a data field value is required.

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

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

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

NameDescription
System_CAPS_pubmethodRequiredAttribute()

Initializes a new instance of the RequiredAttribute class.

NameDescription
System_CAPS_pubpropertyAllowEmptyStrings

Gets or sets a value that indicates whether an empty string is allowed.

System_CAPS_pubpropertyErrorMessage

Gets or sets an error message to associate with a validation control if validation fails.(Inherited from ValidationAttribute.)

System_CAPS_pubpropertyErrorMessageResourceName

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.)

System_CAPS_pubpropertyErrorMessageResourceType

Gets or sets the resource type to use for error-message lookup if validation fails.(Inherited from ValidationAttribute.)

System_CAPS_protpropertyErrorMessageString

Gets the localized validation error message.(Inherited from ValidationAttribute.)

System_CAPS_pubpropertyRequiresValidationContext

Gets a value that indicates whether the attribute requires validation context.(Inherited from ValidationAttribute.)

System_CAPS_pubpropertyTypeId

When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)

NameDescription
System_CAPS_pubmethodEquals(Object)

This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)

System_CAPS_protmethodFinalize()

Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)

System_CAPS_pubmethodFormatErrorMessage(String)

Applies formatting to an error message, based on the data field where the error occurred. (Inherited from ValidationAttribute.)

System_CAPS_pubmethodGetHashCode()

Returns the hash code for this instance.(Inherited from Attribute.)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_pubmethodGetValidationResult(Object, ValidationContext)

Checks whether the specified value is valid with respect to the current validation attribute.(Inherited from ValidationAttribute.)

System_CAPS_pubmethodIsDefaultAttribute()

When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)

System_CAPS_pubmethodIsValid(Object)

Checks that the value of the required data field is not empty.(Overrides ValidationAttribute.IsValid(Object).)

System_CAPS_protmethodIsValid(Object, ValidationContext)

Validates the specified value with respect to the current validation attribute.(Inherited from ValidationAttribute.)

System_CAPS_pubmethodMatch(Object)

When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)

System_CAPS_protmethodMemberwiseClone()

Creates a shallow copy of the current Object.(Inherited from Object.)

System_CAPS_pubmethodToString()

Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubmethodValidate(Object, String)

Validates the specified object.(Inherited from ValidationAttribute.)

System_CAPS_pubmethodValidate(Object, ValidationContext)

Validates the specified object.(Inherited from ValidationAttribute.)

NameDescription
System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfoCount(UInt32)

Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from Attribute.)

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.

System_CAPS_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;

}

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 3.0

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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