Data Validation

Data validation is the process of ensuring that a program operates on clean, correct and useful data. Most .NET developers use Data Annotation Validators. But nopCommerce uses Fluent Validation. It's a small validation library for .NET that uses a fluent interface and lambda expressions for building validation rules for your business objects. 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 source code below to get an idea:

   public class AddressValidator : BaseNopValidator<AddressModel>
   {
       public AddressValidator(ILocalizationService localizationService)
       {
           RuleFor(x => x.FirstName)
           .NotEmpty()
           .WithMessage(localizationService.GetResource("Admin.Address.Fields.FirstName.Required"))
           .When(x => x.FirstNameEnabled && x.FirstNameRequired);
       }
   }
   

2. Annotate your model class with the ValidatorAttribute. Refer to the example below for guidance.

   [Validator(typeof(AddressValidator))]
   public partial class AddressModel : BaseNopEntityModel
   {
     //...
   }
   

   ASP.NET Core will execute the appropriate validator when a view model is posted to a controller.