NorthwindContext context = new NorthwindContext();
var data = context.Categories.ToList();
//序列化
DataContractJsonSerializer serializer = new DataContractJsonSerializer(data.GetType());
using (MemoryStream stream = new MemoryStream())
{
    serializer.WriteObject(stream, data);
    Console.WriteLine(Encoding.UTF8.GetString(stream.ToArray()));
}

using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using ConsoleApplication1.Models.Mapping;

namespace ConsoleApplication1.Models
{
    public class NorthwindContext : DbContext
    {
        static NorthwindContext()
        {
            Database.SetInitializer<NorthwindContext>(null);
        }

        public NorthwindContext()
            : base("Name=NorthwindContext")
        {
            this.Configuration.ProxyCreationEnabled = false;
        }

        public DbSet<Category> Categories { get; set; }
        public DbSet<Product> Products { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new CategoryMap());
            modelBuilder.Configurations.Add(new ProductMap());
        }
    }
}