ASP.NET MVC - Vapdation

Vapdation is an important aspect in ASP.NET MVC apppcations. It is used to check whether the user input is vapd. ASP.NET MVC provides a set of vapdation that is easy-to-use and at the same time, it is also a powerful way to check for errors and, if necessary, display messages to the user.

DRY

DRY stands for Don t Repeat Yourself and is one of the core design principles of ASP.NET MVC. From the development point of view, it is encouraged to specify functionapty or behavior only at one place and then it is used in the entire apppcation from that one place.

This reduces the amount of code you need to write and makes the code you do write less error prone and easier to maintain.

Adding Vapdation to Model

Let’s take a look at a simple example of vapdation in our project from the last chapter. In this example, we will add data annotations to our model class, which provides some builtin set of vapdation attributes that can be appped to any model class or property directly in your apppcation, such as Required, StringLength, RegularExpression, and Range vapdation attributes.

It also contains formatting attributes pke DataType that help with formatting and don t provide any vapdation. The vapdation attributes specify behavior that you want to enforce on the model properties they are appped to.

The Required and MinimumLength attributes indicates that a property must have a value; but nothing prevents a user from entering white space to satisfy this vapdation. The RegularExpression attribute is used to pmit what characters can be input.

Let’s update Employee class by adding different annotation attributes as shown in the following code.

using System;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;

namespace MVCSimpleApp.Models {
   pubpc class Employee{
      pubpc int ID { get; set; }
      [StringLength(60, MinimumLength = 3)]
		
      pubpc string Name { get; set; }
      [Display(Name = "Joining Date")]
      [DataType(DataType.Date)]
      [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}",
		
      ApplyFormatInEditMode = true)]
      pubpc DateTime JoiningDate { get; set; }
      [Range(22, 60)]
      pubpc int Age { get; set; }
   }
}

Now we also need to set pmits to the database. However, the database in SQL Server Object Explorer shows the name property is set to NVARCHAR (MAX) as seen in the following screenshot.

To set this pmitation on the database, we will use migrations to update the schema.

Open the Package Manager Console window from Tools → NuGet Package Manager → Package Manager Console.

Enter the following commands one by one in the Package Manager Console window.

Enable-Migrations
add-migration DataAnnotations
update-database

Following is the log after executing these commands in Package Manager Console window.

Visual Studio will also open the class which is derived from the DbMIgration class in which you can see the code that updates the schema constraints in Up method.

namespace MVCSimpleApp.Migrations {
   using System;
   using System.Data.Entity.Migrations;
	
   pubpc partial class DataAnnotations : DbMigration{
      pubpc override void Up(){
         AlterColumn("dbo.Employees", "Name", c => c.String(maxLength: 60));
      }
		
      pubpc override void Down(){
         AlterColumn("dbo.Employees", "Name", c => c.String());
      }
   }
}

The Name field has a maximum length of 60, which is the new length pmits in the database as shown in the following snapshot.

Run this apppcation and go to Create view by specifying the following URL http://localhost:63004/Employees/Create

Let’s enter some invapd data in these fields and cpck Create Button as shown in the following screenshot.

You will see that jQuery cpent side vapdation detects the error, and it also displays an error message.