EF4.1 使用按层次结构表继承创建数据库时出现异常

我创建了一个非常简单的项目来演示每个层次结构表的继承。在我尝试生成数据库的单元测试中，根据配置，我收到了许多错误之一：

没有Required() method

Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false));
Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true));

提供：

System.Data.DataException : An exception occurred while initializing the database. See the InnerException for details.
  ----> System.Data.EntityCommandCompilationException : An error occurred while preparing the command definition. See the inner exception for details.
  ----> System.Data.MappingException : 
(6,10) : error 3032: Problem in mapping fragments starting at line 6:Condition member 'User.IsActive' with a condition other than 'IsNull=False' is mapped. Either remove the condition on User.IsActive or remove it from the mapping.

与Required() method:

Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false).IsRequired());

Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true).IsRequired());

提供：

System.Data.DataException : An exception occurred while initializing the database. See the InnerException for details.
  ----> System.Data.EntityCommandCompilationException : An error occurred while preparing the command definition. See the inner exception for details.
  ----> System.Data.MappingException : 
(6,10) : error 3023: Problem in mapping fragments starting at lines 6, 13, 19:Column User.IsActive has no default value and is not nullable. A column value is required to store entity data.

据我了解，我们不应该在基本类型上定义鉴别器列/属性，但无论哪种方式，定义或不定义列似乎都没有区别：

  public class User
  {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public virtual int Id { get; set; }

    [Required]
    public virtual string Username { get; set; }

    [Required]
    [DefaultValue(true)]
    public bool IsActive { get; set; } //have tried without this property
  }

  public class InActiveUser : User
  {
    public virtual DateTime DeActivatedDate { get; set; }
  }

  public class ActiveUser : User
  {
  }

您无法将鉴别器映射为实体中的属性。鉴别器定义实体的类型。原因很明显 - 判别器定义了实例化类型。如果您能够在运行时更改鉴别器值，会发生什么情况？ .NET 应如何更改实例化对象的类型？

将实体定义为：

public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public virtual int Id { get; set; }

    [Required]
    public virtual string Username { get; set; }
}

public class InActiveUser : User
{
    public virtual DateTime DeActivatedDate { get; set; }
}

public class ActiveUser : User
{ }

这应该有效：

modelBuilder.Entity<User>()
            .Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false))
            .Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true));