Data validation framework at entity level using Data Annotations

Introduction

This article is all about creating a simple data validation framework on entities using Data Annotation.

Background

Leave aside the business rule validation for a while, ever wondered on how to do data validation with the help of Data Annotations at the entity level? Here is a simple framework to achieve what we are thinking of now ;-)

Using the code

Let us split this whole concept into five small parts:

1. Create a generic entity class and inherit it in all the classes on which we wish to do data validation.

public abstract class Entity
{
	[Required]
    public virtual int Key { get; set; }
}

public class UserAccount : Entity
{
    [Required]
    [StringLength(200)]
    [EmailAddress]
    public virtual string Email { get; set; }

    [Required]
    [StringLength(2)]
    public virtual string FirstName { get; set; }

    [Required]
    [StringLength(2)]
    public virtual string LastName { get; set; }

    [StringLength(20)]
    [RegularExpression(@"^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$",
        ErrorMessage = "Personal phone format is not valid.")]
    public virtual string PersonalPhone { get; set; }
}

2. Create an EntityValidation class which does the actual validation:

public class EntityValidation<T> where T : Entity
{
    public IEnumerable<ValidationResult> Validate(T entity)
    {
        var validationResults = new List<ValidationResult>();
        var validationContext = new ValidationContext(entity, null, null);
        Validator.TryValidateObject(entity,validationContext, validationResults, true);
        return validationResults;
    }
}

3. Create an EntityValidator class which acts as the entry point to use this framework (which in turn uses EntityValidation).

public class EntityValidator
{
    public static IEnumerable<ValidationResult> ValidateEntity<T>(T entity) where T:Entity
    {
        return new EntityValidation<T>().Validate(entity);
    }
} 

4. Use this framework inside the Entity class (that was created in Step-1)

public abstract class Entity
{
	[Required]
    public virtual int Key { get; set; }
 	public virtual IEnumerable<ValidationResult> Validate()
    {
        return EntityValidator.ValidateEntity(this);
    }
}

5. It's time to start using this framework in all our entities (which are derived from Entity):

class Program
{
    static void Main(string[] args)
    {
        var student = new UserAccount() 
        { Email = "sasa.@gmai.com", FirstName = "fn123", 
          LastName = "ln123", PersonalPhone = "1234" };
        foreach (var error in student.Validate())
        {
            Console.WriteLine(error.ErrorMessage);
        }           
    }
} 

The errors would look like this:

errors = Count = 4
[0] = {The Email field is not a valid e-mail address.}
[1] = {The field FirstName must be a string with a maximum length of 2.}
[2] = {The field LastName must be a string with a maximum length of 2.}
[3] = {Personal phone format is not valid.}

Points of Interest

If you would like to know more about Data Annotations, please refer the following MSDN link: http://msdn.microsoft.com/en-us/library/system.componentmodel.dataannotations.aspx.

(This is my first technical article. Please do post your comments to help me improve more.)