Validation Attributes

• Dec 25, 2023
• 7 minutes to read

DevExtreme ASP.NET MVC controls support several validation attributes that reside in the System.ComponentModel.DataAnnotations namespace and other validation attributes:

Attribute	Description	Remarks
Compare	Validates that two properties in a model match.	Built-in
Range	Validates that a property value falls within a specified range.	Built-in
RegularExpression	Validates that a property value matches a specified regular expression.	Built-in
Remote	Performs a remote validation: you call an action method on the server to validate inputs on the client.	Built-in
Required	Validates that a field is not null.	Built-in
StringLength	Validates that a string property value does not exceed a specified length limit.	Built-in
DevExtremeRequired	Validates that a boolean property value is true.	DevExtreme-specific
A custom attribute	You can create a custom validation attribute.

Attach validation attributes to model properties. Refer to Adding Validation in ASP.NET MVC 5 for more information.

Model properties can have multiple attributes. The following code demonstrates the Person model that contains the FirstName property annotated with three validation attributes:

C#

using System.ComponentModel.DataAnnotations;

namespace ApplicationName.Models {
    public class Person {
        [Required(ErrorMessage = "First name is required")]
        [RegularExpression(@"^[a-zA-Z\s]+$", ErrorMessage = "Please, use letters in the first name. Digits are not allowed.")]
        [StringLength(int.MaxValue, MinimumLength = 2, ErrorMessage = "First name must have at least 2 characters")]
        public string FirstName { get; set; }
    }
}

VB

Imports System.ComponentModel.DataAnnotations

Namespace ApplicationName.Models
    Public Class Person
        <Required(ErrorMessage:="First name is required")>
        <RegularExpression("^[a-zA-Z\s]+$", ErrorMessage:="Please, use letters in the first name. Digits are not allowed.")>
        <StringLength(Integer.MaxValue, MinimumLength:=2, ErrorMessage:="First name must have at least 2 characters")>
        Public Property FirstName() As String
    End Class
End Namespace

The attributes are applied when you bind DevExtreme controls to model properties. Refer to Configure Controls to Validate for more information.

Range Attribute

The Range attribute allows you to specify minimum and maximum values for a model property.

If the Range attribute should limit a date or time range, use the attribute overload that accepts a type as the first argument. The date/time values should be strings.

The following code demonstrates how to specify a range for the BirthDate model property:

C#

using System.ComponentModel.DataAnnotations;

namespace ApplicationName.Models {
    public class Person {
        // ...
        [Range(typeof(DateTime), "1/1/1901", "1/1/2016")]
        public DateTime BirthDate { get; set; }
    }
}    

VB

Imports System.ComponentModel.DataAnnotations

Namespace Models
    Public Class Person
        ' ...
        <Range(GetType(DateTime), "1/1/1901", "1/1/2016")>
        Public Property BirthDate() As DateTime
    End Class
End Namespace

Remote Attribute

The Remote attribute allows you to perform remote data validation. You can call an action method on the server to validate inputs on the client.

For example, you can add remote validation for an e-mail input:

1. Create a controller’s action method that checks if a specified e-mail is registered.

   C#

   [HttpPost]
   public IActionResult CheckEmailAddress(string email) {
       if(!_userRepository.VerifyEmail(email)) {
           return Json($"Email {email} is already registered.");
       }
   
       return Json(true);
   }
   

   VB

   <HttpPost>
   Public Function CheckEmailAddress(ByVal email As String) As JsonResult
       If Not _userRepository.VerifyEmail(email) Then
           Return Json($"Email {email} is already registered.")
       End If
   
       Return Json(True)
   End Function
   

2. In a model class, annotate the Email property with the [Remote] attribute, specify a controller’s action method, and a controller’s name.

   C#

   using System.ComponentModel.DataAnnotations;
   
   [Remote("CheckEmailAddress", "Validation")]
   public string Email { get; set; }
   

   VB

   Imports System.ComponentModel.DataAnnotations
   
   <Remote("CheckEmailAddress", "Validation")>
   Public Property Email As String
   

3. Bind the TextBox editor to the Email property. Refer to Validate an Editor for more information.

   Razor C#

   @model ApplicationName.Models.Person
   
   // ...
   
   @Html.DevExtreme().TextBoxFor(model => model.Email)
   

   Razor VB

   @ModelType ApplicationName.Models.Person 
   
   @(Html.DevExtreme().TextBoxFor(Function(model) model.Email))
   

   

Refer to RemoteAttribute Class for more information.

Note

The Editors - Validation and Form - Validation online demos demonstrate how to use the [Remote] attribute.

Required Attribute

The Required attribute allows you to validate that a field is not null.

If you bind controls to non-nullable properties, you can receive the The value ‘’ is invalid error message. Refer to Microsoft Documentation: Required Validation on the Server for more information.

DevExtremeRequired Attribute

The DevExtremeRequired attribute resides in the DevExtreme.AspNet.Mvc namespace and allows you to verify if a boolean value is true. Refer to this blog post for more information on why you should use this attribute instead of the built-in Required attribute.

For example, you can use this attribute for the CheckBox control when you need to check if the control is selected (its value is true).

View

Razor C#

@using(Html.BeginForm("EditPerson", "Home", FormMethod.Post)) {
    @(Html.DevExtreme().Form<Person>()
        .Items(items => {
            // ...
            items.AddSimpleFor(model => model.Accepted)
                .Label(label => label.Visible(false))
                .Editor(editor => editor.CheckBox().Text("I agree to the Terms and Conditions"));
        })
    )
}

Razor VB

@Using (Html.BeginForm("EditPerson", "Home", FormMethod.Post))
    @(Html.DevExtreme().Form(Of Models.Person)() _
        .Items(Sub(items)
            items.AddSimpleFor(Function(model) model.Accepted) _
                .Label(Sub(Label) Label.Visible(False)) _
                .Editor(Function(editor) editor.CheckBox().Text("I agree to the Terms and Conditions"))
        End Sub)
    )
End Using

Model

C#

using System.ComponentModel.DataAnnotations;
using DevExtreme.AspNet.Mvc;

namespace ApplicationName.Models {
    public class Person {
        // ...
        [DevExtremeRequired(ErrorMessage = "You must agree to the Terms and Conditions")]
        public bool Accepted { get; set; }
    }
}    

VB

Imports System.ComponentModel.DataAnnotations
Imports DevExtreme.AspNet.Mvc

Namespace Models
    Public Class Person
        ' ...
        <DevExtremeRequired(ErrorMessage:="You must agree to the Terms and Conditions")>
        Public Property Accepted() As Boolean
    End Class
End Namespace

Custom Attribute

You can implement a custom attribute if built-in validation attributes do not meet your requirements.

The steps below describe how to create the VerifyAge attribute and apply it to the DateBox control. The attribute should check if a person is over the specified age, for example, the age of 21.

1. Create the VerifyAgeAttribute class that implements the validation logic. Duplicate the logic on the client and on the server. To do this, declare the class that is inherited from the ValidationAttribute class and implements the IClientValidatable interface.

   Implement the following methods:

   • IsValid

     Validates data on the server to ensure invalid values are not sent when JavaScript is switched off on the client.

   • GetClientValidationRules

     Adds a validation rule used by DevExtreme client-side validation engine. The rule has the following properties:

     • ErrorMessage - Accepts a formatted validation message.

     • ValidationParameters - Provides access to rule parameters. Use the Add method to add the validationcallback parameter. The parameter should specify a JavaScript function that implements the validation logic.

   • FormatErrorMessage

     Overrides the default FormatErrorMessage method.

   C#

   using System;
   using System.Collections.Generic;
   using System.ComponentModel.DataAnnotations;
   using System.Web.Mvc;
   
   namespace DevExtreme.MVC.Demos.ViewModels {
       public class VerifyAgeAttribute : ValidationAttribute, IClientValidatable {
           public VerifyAgeAttribute(int age) {
               Age = age;
           }
           public int Age { get; private set; }
           protected override ValidationResult IsValid(object value, ValidationContext validationContext) {
               if((DateTime?)value <= DateTime.Now.AddYears(-Age)) {
                   return ValidationResult.Success;
               }
               return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
           }
           IEnumerable<ModelClientValidationRule> IClientValidatable.GetClientValidationRules(ModelMetadata metadata, ControllerContext context) {
               var rule = new ModelClientValidationRule();
               rule.ErrorMessage = FormatErrorMessage(metadata.GetDisplayName());
               rule.ValidationParameters.Add(
                   "validationcallback",
                   $@"function(options) {{
                       var now = new Date();
                       return options.value && options.value <= now.setFullYear(now.getFullYear() - {Age});
                   }}");
               rule.ValidationType = "custom";
               yield return rule;
           }
           public override string FormatErrorMessage(string name) {
               return string.Format(ErrorMessageString, name, Age);
           }
       }
   }
   

   VB

   Imports System.ComponentModel.DataAnnotations
   
   Namespace DevExtreme.MVC.Demos.ViewModels
       Public Class VerifyAgeAttribute
           Inherits ValidationAttribute
           Implements IClientValidatable
   
           Public Sub New(ByVal age As Integer)
               Me.Age = age
           End Sub
   
           Public Property Age As Integer
   
           Protected Overrides Function IsValid(ByVal value As Object, ByVal validationContext As ValidationContext) As ValidationResult
               If CType(value, Date?) <= Date.Now.AddYears(-Age) Then
                   Return ValidationResult.Success
               End If
   
               Return New ValidationResult(FormatErrorMessage(validationContext.DisplayName))
           End Function
   
           Private Function IClientValidatable_GetClientValidationRules(ByVal metadata As ModelMetadata, ByVal context As ControllerContext) As IEnumerable(Of ModelClientValidationRule) Implements IClientValidatable.GetClientValidationRules
               Dim rule = New ModelClientValidationRule()
               rule.ErrorMessage = FormatErrorMessage(metadata.GetDisplayName())
               rule.ValidationParameters.Add("validationcallback", $"function(options) {{
                       var now = new Date();
                       return options.value && options.value <= now.setFullYear(now.getFullYear() - {Age});
                   }}")
               rule.ValidationType = "custom"
               Return {rule}
           End Function
   
           Public Overrides Function FormatErrorMessage(ByVal name As String) As String
               Return String.Format(ErrorMessageString, name, Age)
           End Function
   
       End Class
   End Namespace
   

2. Attach the VerifyAge attribute to a model property and specify an age.

   C#

   using System.ComponentModel.DataAnnotations;
   
   namespace ApplicationName.Models {
       public class Person {
           // ...
           [VerifyAge(21, ErrorMessage = "You must be at least {1} years old")]
           public DateTime? BirthDate { get; set; }
       }
   }
   

   VB

   Imports System.ComponentModel.DataAnnotations
   Namespace Models
       Public Class Person
           ' ...
           <VerifyAge(21, ErrorMessage:="You must be at least {1} years old")>
           Public Property BirthDate() As Date?
       End Class
   End Namespace
   

3. Bind the DateBox control to the BirthDate model property. Refer to Validate an Editor for more information.

   Razor C#

   @model ApplicationName.Models.Person
   
   @(Html.DevExtreme().DateBoxFor(model => model.BirthDate))
   

   Razor VB

   @ModelType ApplicationName.Models.Person
   
   @(Html.DevExtreme().DateBoxFor(Function(model) model.BirthDate))
   

   

Note

Demo: You can find the provided code in the Editors - Validation demo.