Data Validation in MVC

If you work in MVC you will observe that all the model validation is attribute-based. In the past few days I have been working on a website architecture developed in ASP.NET 4.0 where I implemented attribute-based validation of a Data Model. To make the article simple I will explain it here using a console application with simple code. Let's start with a data model class:

public class Model
{
    public string JobName { get; set; }
    public string DeptName { get; set; }
    public string EmpName { get; set; }
}

Here the requirement is that the Job Name Is mandatory and Dept Name is mandatory and its maximum length cannot be greater than 3 . A very obvious way to do it is to check all the conditions using IF-ELSE but It will increase the line of codes one needs to put IF – ELSE everywhere in the model class. To simplify it let's make two custom attributes that will validate the data model.

[AttributeUsage(AttributeTargets.Field|AttributeTargets.Property)]
    public class Requierd:Attribute
    {
        public string ErrorMessage { get; set; }
        public Requierd(string errorMessage)
        {
            this.ErrorMessage = errorMessage;
        }
            }
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
    public class MaxLength : Attribute
    {
        public string ErrorMessage { get; set; }
        public int Length { get; set; }
        public MaxLength(string errorMessage,int MaximumLength)
        {
            this.ErrorMessage = errorMessage;
            this.Length = MaximumLength;
        }
   }

Now we need one more class that will read the property value, validate it and show the Error message through Reflection.

public class EntityBase
{
    public List<string> BrokenRules = null;
    public EntityBase()
    {
        BrokenRules = new List<string>();
    }
    public bool Validate()
    {
        bool IsValid = true;
        PropertyInfo[] PropInfo = this.GetType().GetProperties();
        foreach (PropertyInfo info in PropInfo)
        {
            object data = info.GetValue(this, null);

            foreach (object RequiredAttribute in info.GetCustomAttributes(typeof(Requierd), true))
            {
                if (data == null)
                {
                    IsValid = false;
                    BrokenRules.Add((RequiredAttribute as Requierd).ErrorMessage);
                }
            }
            foreach (object MaxLengthAttribute in info.GetCustomAttributes(typeof(MaxLength), true))
            {
                if (data != null)
                {
                     if (data.ToString().Length > (MaxLengthAttribute as MaxLength).Length)
                     {
                         IsValid = false;
                         BrokenRules.Add((MaxLengthAttribute as MaxLength).ErrorMessage.ToString());

                    }
                }
             }
         }
         return IsValid;
     }
}

Until now our Validation Attribute is ready, The Entity Base class is ready to validate . Let's return to the model class where we will implement it.

public class Model : EntityBase
{
    [Requierd("Job Name Is Requierd")]
    public string JobName { get; set; }
    [Requierd("DeptName Is Requierd")]
    [MaxLength("DeptName should not be greater than 3",3)]
    public string DeptName { get; set; }
    public string EmpName { get; set; }
}

Time to initialize the model class from the Main class and call the validation function.

static void Main(string[] args)
{
    Model obj = new Model();
    obj.JobName = "Coder";
    obj.DeptName = "Computer Science";
    if (!obj.Validate())
    {
        foreach (string message in obj.BrokenRules)
        {
           Console.WriteLine(message);
        }
    }
    Console.Read();
}

In the Model class we have put the required attribute on JobName and DeptName and MaxLength attribute with max Length of 3 on Dept name, the Required attribute will successfully pass through but the Max Length Validation will fail because the length of Computer Science is more than 3.