Use of FluentValidation for creating a sophisticated data validation framework in ASP.NET MVC

Data validation is quite critical when it comes to usability and data integrity of any software or application. It helps in improving the quality of the data as well as it ensures the data consistency. Data annotations is still one of the most popular ways to do model validation in ASP.NET MVC. But, a lot of developers and projects are leaning towards Fluent Validation library these days. Why? Well, Fluent Validation is quite versatile and offers advantages like:

- Easy for unit test validation rules

- Option to split the validation rules completely from the model

Again, there is nothing wrong in data annotations as similar results can be accomplished by following that approach. But, too many annotations can make your model look quite ugly. 


What is Fluent Validation?

Fluent Validation is a small validation library for .NET that uses a fluent interface and lambda expressions for building validation rules. Download Here: https://github.com/JeremySkinner/FluentValidation


In this article, we will go over the process of implementing Fluent Validation in ASP.NET web application. For this, we are going to take a sample web application that includes a Product Model and views for adding, editing and deleting the products from the product table. 

First, we need to download the FluentValidation package from NuGet. We can do so by going to Package Manager Console and entering the following command: Install-Package FluentValidation.MVC5





Here is the example of our current Product Model where we have all the properties defined:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using FluentValidation;
using FluentValidation.Attributes;
using FluentValidation.Results;
using System.ComponentModel.DataAnnotations;
using EFCodeFirstMVCApplication.Models;
 
 
namespace EFCodeFirstMVCApplication.Models
{
 
 
    public class Product
    {
        public int ID { get; set; }
 
 
        public string Prod_SKU { get; set; }
        public string Prod_Name { get; set; }
        public DateTime CreateDate { get; set; }
 
     }
 
}



In order to implement FluentValidation, we need to add a line to the Global.asax file (in Application _Start method). This will hook up FluentValidation class library to the ASP.NET MVC 5 validation framework. We will call FluentValidationModelValidatorProvider.Configure() method inside the global.asax file like this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;
using FluentValidation.Mvc;
 
namespace EFCodeFirstMVCApplication
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
 
           // Adding FluentValidation
            FluentValidationModelValidatorProvider.Configure();
        }
    }
}



Now, we can start setting up the actual data validation. There are two ways of creating custom validators. The first is to create a custom property validator, the second is to make use of the Custom method on AbstractValidator. Let’s create a new class called “FluentProductValidator” like this:

public class FluentProductValidator : AbstractValidator<Product>
 
     {
           public FluentProductValidator()
 
        {
 
        }
     }



Next step is to add validation rules in the FluentProductValidator class for “Prod_SKU” & “Prod_Name”.

public class FluentProductValidator : AbstractValidator<Product>
 
     {
           public FluentProductValidator()
 
        {
 
            RuleFor(x => x.Prod_SKU).NotEmpty().WithMessage("SKU is required");
            RuleFor(x => x.Prod_Name).NotEmpty().WithMessage("Name is required");
             
        }
     }



Our complete Product Model files looks like this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using FluentValidation;
using FluentValidation.Attributes;
using FluentValidation.Results;
using System.ComponentModel.DataAnnotations;
using EFCodeFirstMVCApplication.Models;
 
 
namespace EFCodeFirstMVCApplication.Models
{
 
 
[Validator(typeof(FluentProductValidator))]
    public class Product
    {
        public int ID { get; set; }
 
 
        public string Prod_SKU { get; set; }
        public string Prod_Name { get; set; }
        public DateTime CreateDate { get; set; }
 
        public virtual ICollection<ProductManufacturerMapping> ProductCategoryMappings { get; set; }
    }
 
  
 
 
     public class FluentProductValidator : AbstractValidator<Product>
 
     {
           public FluentProductValidator()
 
        {
 
            RuleFor(x => x.Prod_SKU).NotEmpty().WithMessage("SKU is required");
            RuleFor(x => x.Prod_Name).NotEmpty().WithMessage("Name is required");
             
        }
     }
 
}


Now, if we run the application and go to Create OR Edit, we should see the validations like this:



We have successfully implemented the FluentValidation in our ASP.NET MVC web application.



Open-source .NET projects like nopCommerce are using FluentValidation for data validation
FluentValidation is a very powerful validation framework that allows many features that regular ComponentModel framework does not offer which is why project like nopCommerce is using it in the official software. Now the question is, Fluent Validation benefits projects like nopCommerce?

- Fluent Validation gives nopCommerce far more control over the validation rules

- nopCommerce project can make use of conditional validation which is quite easier as compared to data annotations

- It allows nopCommerce an option to separate all the validations from the view models

- Unit testing is far easier as compared to data annotations

- Fluent Validation offers a better client-side validation support

 

Let’s take a look at how nopCommerce is making use of FluentValidation in the project

One of the most important thing in an e-Commerce business is customer data. In order to maintain quality data (i.e. customer information) in the database, it is critical to have strong data validation rules on the public store. nopCommerce makes the best use of Fluent Validation in this area so let’s look into “AddressValidator.cs” that can be found in this location:

Nop.Web\Validators\Common\AddressValidator.cs


Here is the source code:

using FluentValidation;
using FluentValidation.Results;
using Nop.Core.Domain.Common;
using Nop.Services.Directory;
using Nop.Services.Localization;
using Nop.Web.Framework.Validators;
using Nop.Web.Models.Common;
 
namespace Nop.Web.Validators.Common
{
    public class AddressValidator : BaseNopValidator<AddressModel>
    {
        public AddressValidator(ILocalizationService localizationService,
            IStateProvinceService stateProvinceService,
            AddressSettings addressSettings)
        {
            RuleFor(x => x.FirstName)
                .NotEmpty()
                .WithMessage(localizationService.GetResource("Address.Fields.FirstName.Required"));
            RuleFor(x => x.LastName)
                .NotEmpty()
                .WithMessage(localizationService.GetResource("Address.Fields.LastName.Required"));
            RuleFor(x => x.Email)
                .NotEmpty()
                .WithMessage(localizationService.GetResource("Address.Fields.Email.Required"));
            RuleFor(x => x.Email)
                .EmailAddress()
                .WithMessage(localizationService.GetResource("Common.WrongEmail"));
            if (addressSettings.CountryEnabled)
            {
                RuleFor(x => x.CountryId)
                    .NotNull()
                    .WithMessage(localizationService.GetResource("Address.Fields.Country.Required"));
                RuleFor(x => x.CountryId)
                    .NotEqual(0)
                    .WithMessage(localizationService.GetResource("Address.Fields.Country.Required"));
            }
            if (addressSettings.CountryEnabled && addressSettings.StateProvinceEnabled)
            {
                Custom(x =>
                {
                    //does selected country has states?
                    var countryId = x.CountryId.HasValue ? x.CountryId.Value : 0;
                    var hasStates = stateProvinceService.GetStateProvincesByCountryId(countryId).Count > 0;
 
                    if (hasStates)
                    {
                        //if yes, then ensure that state is selected
                        if (!x.StateProvinceId.HasValue || x.StateProvinceId.Value == 0)
                        {
                            return new ValidationFailure("StateProvinceId", localizationService.GetResource("Address.Fields.StateProvince.Required"));
                        }
                    }
                    return null;
                });
            }
            if (addressSettings.CompanyRequired && addressSettings.CompanyEnabled)
            {
                RuleFor(x => x.Company).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.Company.Required"));
            }
            if (addressSettings.StreetAddressRequired && addressSettings.StreetAddressEnabled)
            {
                RuleFor(x => x.Address1).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.StreetAddress.Required"));
            }
            if (addressSettings.StreetAddress2Required && addressSettings.StreetAddress2Enabled)
            {
                RuleFor(x => x.Address2).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.StreetAddress2.Required"));
            }
            if (addressSettings.ZipPostalCodeRequired && addressSettings.ZipPostalCodeEnabled)
            {
                RuleFor(x => x.ZipPostalCode).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.ZipPostalCode.Required"));
            }
            if (addressSettings.CityRequired && addressSettings.CityEnabled)
            {
                RuleFor(x => x.City).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.City.Required"));
            }
            if (addressSettings.PhoneRequired && addressSettings.PhoneEnabled)
            {
                RuleFor(x => x.PhoneNumber).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.Phone.Required"));
            }
            if (addressSettings.FaxRequired && addressSettings.FaxEnabled)
            {
                RuleFor(x => x.FaxNumber).NotEmpty().WithMessage(localizationService.GetResource("Account.Fields.Fax.Required"));
            }
        }
    }
}



All the validation rules in nopCommerce are making use of localization resource values so that depending on the selected language for public store, the validation messages can be shown. If we look closely to the source code (above), we will find that nopCommerce is using “NotEmpty” validator (in this case) instead of NotNull validator.  Whereas, in QueuedEmailValidator.cs, nopCommerce project is making use of “NotNull() validator”:





using FluentValidation;
using Nop.Admin.Models.Messages;
using Nop.Services.Localization;
using Nop.Web.Framework.Validators;
 
namespace Nop.Admin.Validators.Messages
{
    public class QueuedEmailValidator : BaseNopValidator<QueuedEmailModel>
    {
        public QueuedEmailValidator(ILocalizationService localizationService)
        {
            RuleFor(x => x.From).NotEmpty().WithMessage(localizationService.GetResource("Admin.System.QueuedEmails.Fields.From.Required"));
            RuleFor(x => x.To).NotEmpty().WithMessage(localizationService.GetResource("Admin.System.QueuedEmails.Fields.To.Required"));
 
            RuleFor(x => x.SentTries).NotNull().WithMessage(localizationService.GetResource("Admin.System.QueuedEmails.Fields.SentTries.Required"))
                                    .InclusiveBetween(0, 99999).WithMessage(localizationService.GetResource("Admin.System.QueuedEmails.Fields.SentTries.Range"));
 
        }
    }
}



So, what is the difference between these two validators?
FluentValidation ships with several built-in validators. The error message for each validator can contain special placeholders that will be filled in when the error message is constructed.

NotNull Validator
Description: Ensures that the specified property is not null.

Example:
RuleFor(customer => customer.Surname).NotNull();

Example error: 'Surname' must not be empty. String format args:

{PropertyName} = The name of the property being validated
{PropertyValue} = The current value of the property



NotEmpty Validator
Description: Ensures that the specified property is not null, an empty string or whitespace (or the default value for value types, eg 0 for int)

Example:
RuleFor(customer => customer.Surname).NotEmpty();

Example error: 'Surname' should not be empty. String format args:

{PropertyName} = The name of the property being validated
{PropertyValue} = The current value of the property

For more information, please refer: FluentValidation Wiki


How to change/update data validation message in nopCommerce?

Option 1: A good rule of thumb in managing localization resource values is from the administration section. If you are updating any existing value, it should be done from the administrator section (for all languages). And, if you are adding a new message on your site, a proper way to add it is via adding a new localization resource value for each language. This way, you will never have to touch the code while updating the values.

Let’s say we would like to change the message for:

RuleFor(x => x.FirstName)
                .NotEmpty()
                .WithMessage(localizationService.GetResource("Address.Fields.FirstName.Required"));


We should change/update it in the administration section (for each language): Configuration > Languages





Now, if we go to the nopCommerce public store (in account) and try to add the address without first name, we should see the updated message like this:






Option 2: An alternative method to change/update the validation method in nopCommerce is to update directly in the source code. This is not the cleanest approach as in future if you wish you update it again, you will have to change it in the source code. But, at the end of the day this method still works and get the job done.

Go to: Nop.Web\Validators\Common\AddressValidator.cs

Original code:

RuleFor(x => x.FirstName)
                .NotEmpty()
                .WithMessage(localizationService.GetResource("Address.Fields.FirstName.Required"));


New updated validation message in the code:

RuleFor(x => x.FirstName)
                .NotEmpty()
                .WithMessage("New Hardcoded Validation Message Here");


Now, if we go to the nopCommerce public store (in account) and try to add the address without first name, we should see the updated message like this:




Resources:

You can download nopCommerce here: http://www.nopcommerce.com/

nopCommerce Version (used in this article): Version 3.70

About Author

Written By Lavish Kumar

Based out of New York, USA, Lavish Kumar is a full stack web developer by profession and founder of Striving Programmers, a trusted community for developers that offers a wealth of articles and forums to assist individuals with improving their software development skills.

Leave your comment
Comments
10/7/2016 5:09 AM
How did you get it working with injection?

AddressValidator

public AddressValidator(ILocalizationService localizationService,
            IStateProvinceService stateProvinceService,
            AddressSettings addressSettings)
?
10/7/2016 8:12 AM
Have you looked into "Nop.Web\Validators\Common\AddressValidator.cs" as I mentioned above in the article?

Are you facing any issues?
11/10/2016 12:06 PM
I too had issues with using DI and FluentValidation.
The other user was eluding to an error that is generated
when you don't have a parameter-less constructor. How
did you get around that issue in your AddressValidator?
11/10/2016 12:44 PM
Hi Yale,

I would just like to clarify one thing - Are you talking about "Option 2" above in which I am updating the validation message in the source code?

Please clarify what you are referring to?
11/10/2016 1:15 PM
Thanks for the reply. I'm referring to how you implemented the
AddressValidator using Dependency Injection.

public AddressValidator(ILocalizationService localizationService,
            IStateProvinceService stateProvinceService,
            AddressSettings addressSettings)

When doing so with FluentValidation, this throws an error because
FluentValidation is looking for a ctor w/o parameters.

Thanks
11/10/2016 2:38 PM
Hi Yale,

I am not implementing AddressValidator in the above article. I am basically giving an overview of how FluentValidation is being used in nopCommerce. What you are referring to is not complete code. You can simply refer to "Nop.Web\Validators\Common\AddressValidator.cs" in your nopCommerce project and see the full source code.

You have to complete two steps in order to add a validation to some models in nopCommerce:

1. Create a class derived from AbstractValidator class and put all required logic there. See the image below to get an idea:
   public class AddressValidator : AbstractValidator<AddressModel>
    {
        public AddressValidator(ILocalizationService localizationService)
        {
            RuleFor(x => x.FirstName)
                .NotEmpty()
                .WithMessage(localizationService.GetResource("Address.Fields.FirstName.Required"));
        }
    }


2. Annotate your model class with the ValidatorAttribute. Refer to the example below for guidance.
    [Validator(typeof(AddressValidator))]
    public class AddressModel : BaseNopEntityModel
    {

ASP.NET will execute the appropriate validator when a view model is posted to a controller.
11/10/2016 2:43 PM
Look into the following:

- Nop.Web\Validators\Common\AddressValidator.cs
- Nop.Web\Models\Common\AddressModel.cs
11/10/2016 2:54 PM
You can pass ILocalization Service as a parameter to the class constructor and nopCommerce will see the paramater. Then nopCommerce dependency injection engine will be used with an instance to Localization Service.

As you can see in the above code, GetResource method of Localization Service is used that retrieves a string resource which is then passed into the .WithMessage method.

Hope it helps!