.net 自创建数据库以来，支持 上下文的模型已更改

错误消息:

"自数据库创建以来，支持"AddressBook"上下文的模型已更改.请手动删除/更新数据库，或使用IDatabaseInitializer实例调用database.SetInitializer.例如，RecreateDatabaseIfModelChanges策略将自动删除并重新创建数据库，并可以 Select 使用新的d为其种子."阿塔."

我正在try 使用代码优先功能，下面是我写的:

var modelBuilder = new ModelBuilder();
var model = modelBuilder.CreateModel();
using (AddressBook context = new AddressBook(model))
{
    var contact = new Contact
    {
        ContactID = 10000,
        FirstName = "Brian",
        LastName = "Lara",
        ModifiedDate = DateTime.Now,
        AddDate = DateTime.Now,
        Title = "Mr."

    };
    context.contacts.Add(contact);
    int result = context.SaveChanges();
    Console.WriteLine("Result :- "+ result.ToString());
}

上下文类:

public class AddressBook : DbContext
{
    public AddressBook()
    { }
    public AddressBook(DbModel AddressBook)
        : base(AddressBook)
    {

    }
    public DbSet<Contact> contacts { get; set; }
    public DbSet<Address> Addresses { get; set; }
}

以及连接字符串:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
    <add name="AddressBook" providerName="System.Data.SqlClient"  
         connectionString="Data Source=MyMachine;Initial Catalog=AddressBook;
         Integrated Security=True;MultipleActiveResultSets=True;"/>
    </connectionStrings>
</configuration>

因此，数据库名为"AddressBook"，当我试图将contact对象添加到上下文中时，会发生错误.我有什么遗漏吗？