Update existing entity from database

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MVC4

entity-framework

Hi i have an entity and i am gonna add two tables named as country and state.
There is a relation between these two tables based on CountryId.
I used the "Update Model from database ..." to add these two entity types.
But I getting an error "The entity type Country is not part of the model for the current context.".

I have manually written two classes for these two entity-types given as below:-

public partial class Country
{
    //[Key]    //[DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public int CountryID { get; set; }
    public string CountryName { get; set; }
}

public partial class State
{
    public int StateID { get; set; }
    public string StateName { get; set; }
    public int CountryID { get; set; }
}

and

public DbSet<Country> Countries { get; set; }
public DbSet<State> States { get; set; }

Controller to fetch coutries and states :-

public JsonResult GetCountries()
    {
        List<Country> allCountry = new List<Country>();
        using (SunilEntities dc = new SunilEntities())
        {
            allCountry = dc.Countries.OrderBy(a => a.CountryName).ToList();
        }
        return new JsonResult { Data = allCountry, JsonRequestBehavior =       JsonRequestBehavior.AllowGet };
    }

public JsonResult GetStates(int countryID)
       {
           List<State> allState = new List<State>();
           using (SunilEntities dc = new SunilEntities())
           {
               allState = dc.States.Where(a => a.CountryID.Equals(countryID)).OrderBy(a => a.StateName).ToList();
           }
           return new JsonResult { Data = allState, JsonRequestBehavior = JsonRequestBehavior.AllowGet };
       }

What should be the exact classes to be used to use these two tables in my controller?
Is there any way I can get automated classes after entity being updated with newer tables?

What I have tried:

public partial class Country
{
[Key] [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
public int CountryID { get; set; }
public string CountryName { get; set; }
}

public partial class State
{
public int StateID { get; set; }
public string StateName { get; set; }
public int CountryID { get; set; }
}