public class User :  IValidatableObject
{
    public string Name{get;set;}

    [Required]
    public DateTime CreationDate{get;set;}

    public DateTime UpdatedOnDate{get;set;}

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if(Name="abc")
        {
            yield return new ValidationResult("please choose any other name then abc", new[] { "Name" });
        }
    }
}

User u = new User();
u.Name = "Some name";
u.CreationDate = DateTime.Now
dbContext.Users.Add(u);
dbContext.SaveChanges();

// class structure that I am looking for
public class User : IValidatableObject,IMyCustomInterFace
{
    //rest codes as above class

    public void MyMethod(Whatever)
    {
        //this method gets called after Validate() and before save

        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Added)
        {
            //add creation date_time
            this.CreationDate=DateTime.Now;

            //SET MORE DEFAULTS
        }

        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Modified)
        {
            //update Updation time
            this.UpdatedOnDate=DateTime.Now;
        }
    }
}

User u = new User();
u.Name = "Some name";
dbContext.Users.Add(u);
dbContext.SaveChanges();

User u = getUserFromSomeWhere();
u.Name = "Updated Name";
dataContext.Entry<User>(u).State = System.Data.EntityState.Modified;
dbContext.SaveChanges();

public interface IHasTimeStamp
{
    void DoTimeStamp();
}

Public class User : IHasTimeStamp
(
    public void DoTimeStamp()
    {
        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Added)
        {
            //add creation date_time
            this.CreationDate=DateTime.Now;
        }

        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Modified)
        {
            //update Updation time
            this.UpdatedOnDate=DateTime.Now;
        }
    }
}

public partial class MyEntities
{
    partial void OnContextCreated()
    {
        // Register the handler for the SavingChanges event.
        this.SavingChanges
            += new EventHandler(context_SavingChanges);
    }

    // SavingChanges event handler.
    private static void context_SavingChanges(object sender, EventArgs e)
    {
        // Validate the state of each entity in the context
        // before SaveChanges can succeed.
        foreach (ObjectStateEntry entry in
            ((ObjectContext)sender).ObjectStateManager.GetObjectStateEntries(EntityState.Added | EntityState.Modified))
        {
            if (!entry.IsRelationship && (entry.Entity is IHasTimeStamp))
            {
            (entry.Entity as IHasTimeStamp).DoTimeStamp();
            }
        }
    }
}