How to validate an input against a changing validation requirements

 

Introduction

Data annotation is a server side mechanism that is used to validate a certain model attribute value in MVC.It binds a model attribute to a certain validation attribute type .Common validation attribute types include

• Required
• Range
• DataType
• Regular expression
• ....

Regular expression data annotation is used to validate a model attribute value against a certain pattern,as example below

The following data annotation checks if a model attribute value qualifies to be a valid e-mail address

[RegularExpression(@"^\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$", ErrorMessage = "Email is not valid.")]

The model attributes are bound to the proper data annotation while creating the model

<>

What if the pattern is subject to change as per user requirements

for example user can control the complexity degree of user passwords

	 public partial class PasswordComplexityRuleDataModel
    {
        public int Id { get; set; }
        public bool MustContainLettersNumbers { get; set; }
        public bool MustContainSpecialCharacters { get; set; }
        public bool MustContainUpperLower { get; set; }
        public short MinLength { get; set; }
       
    }

Solution 1

call a certain validation function on each action marked as (post) Example

1. model

   				public partial class UserDataModel
       {
   
   
         /**/
   
   				public string passwordinvalid { get; set; }
   
       }
   			..

2. Controller

   		
   		
   		
   				   public IActionResult Save(UserDataModel user)
           {
               //if(PasswrodRequirementAreMet(user.Password))
               //{
               //ModelState.AddModelError("passwordinvalid", "");
                //                         ||
   			//                          add a span bound to this property in view}
               if (ModelState.IsValid)
               {
                   _userServiceInterface.SaveUser(user);
                   return RedirectToAction(nameof(Index));
               }
               return View(user);
           }
   		..
   		

This solution has a drawback of calling it on every action of type (post)

Solution 2

1. Create a custom validation attribute to take care of validating the input

   //
   
   
    class CustomPassWordValidation:ValidationAttribute
    {
      protected override ValidationResult IsValid(object value, ValidationContext validationContext)
           {
   		  PasswordValid = CheckPasswordAgainstPasswordSettings(value.ToString());
   			  
   				if (PasswordValid != "password valid")
   				{
   						ErrorMessage = PasswordValid;
   					return new ValidationResult(ErrorMessage);
   				}
   				return ValidationResult.Success;
   		}
   		 string CheckPasswordAgainstPasswordSettings(string password)
           {
   			/**/
   			return "password valid";
   		}
   }
   
   ...

2. In the data model containing your attribute,bind the attribute to the attribute validator created above

   	 public class UserViewModel
       {
   	[CustomValidationAttribute.CustomPassWordValidation(ErrorMessage ="travesh")]
   	   public string Password { get; set; }
   	   ..

   }

• If your coding standards follows the dependency injection supporting nature of asp.net core mvc,the function checking password validity may be calling a function in another interface
• you can call the interface instance using the following syntax

//


 class CustomPassWordValidation:ValidationAttribute
 {
 // an object type (service interface type ) 
  protected IPasswordComplexityRuleService _passwordComplexityRuleService 
  
   protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
		  //call the interface instance
		 _passwordComplexityRuleService =(IPasswordComplexityRuleService) validationContext.GetService(typeof(IPasswordComplexityRuleService));
		  PasswordValid = CheckPasswordAgainstPasswordSettings(value.ToString());
			  
				if (PasswordValid != "password valid")
				{
						ErrorMessage = PasswordValid;
					return new ValidationResult(ErrorMessage);
				}
				return ValidationResult.Success;
		}
		 string CheckPasswordAgainstPasswordSettings(string password)
        {
			/*interface instance is used here*/
			return "password valid";
		}
}

...