using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.Migrations;
using System.Linq;
using System.ComponentModel.DataAnnotations;

using CodeFirstEntity.Models;  // import tables models
using CodeFirstEntity.Migrations;

namespace CodeFirstEntity
{
    public class ApiEntity : DbContext
    {
        public ApiEntity() : base("TestDB")
        {
            Database.SetInitializer(new MigrateDatabaseToLatestVersion<ApiEntity, Configuration>());
        }

...