循环和多级联路径使用EF代码优先

我很困惑!!这是我第一次使用MVC3和EF Code first。我得到以下错误:

引入外键约束FK_dbo.CityUsers_dbo。表'CityUsers'上的Cities_CityID'可能导致循环或多个级联路径。指定ON DELETE NO ACTION或ON UPDATE NO ACTION，或修改其他外键约束。无法创建约束。

我已经工作了几个小时，尽我所能，但就是无法处理它!

这个场景是，有一个Man类，从这个类派生出User。每个用户只属于一个城市。这里的用户是指管理员用户。每个用户都可以插入/更新多个城市，并且每个城市一次只能由一个用户修改。我已经创建了第三个名为'CityUser'的表来跟踪修改City记录的用户。

这是我的模型类:

public class Man
{
    [Key]
    [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public long ID { get; set; }
    //------------------------------------------------------------//
    [Required, MaxLength(20)]
    [LocalizedAttribute("FName")]
    public string FName { get; set; }
    //------------------------------------------------------------//
    [Required, MaxLength(20)]
    [LocalizedAttribute("LastName")]
    public string LastName { get; set; }
    //------------------------------------------------------------//
    [Required]
    [RegularExpression("^[0-9]+$", ErrorMessageResourceName = "ErrorOnlyNumbers", ErrorMessageResourceType = typeof(MAHAL_E_MA_Model.Properties.Resources))]
    [LocalizedAttribute("Mobile")]
    public string Mobile { get; set; }
    //------------------------------------------------------------//
    [LocalizedAttribute("Phone")]
    [RegularExpression("^[0-9]+$", ErrorMessageResourceName = "ErrorOnlyNumbers", ErrorMessageResourceType = typeof(MAHAL_E_MA_Model.Properties.Resources))]
    public string HomePhone { get; set; }
    //------------------------------------------------------------//
    [RegularExpression("^[0-9]+$")]
    [LocalizedAttribute("IDCardNumber")]
    public string IDCardNumber { get; set; }
    //------------------------------------------------------------//
    [RegularExpression("^[0-9]+$")]
    [LocalizedAttribute("NationalCode")]
    public string NationalCode { get; set; }
    //------------------------------------------------------------//
    [MaxLength(10)]
    [LocalizedAttribute("DOB")]
    public int DOB { get; set; }
    //------------------------------------------------------------//
    [Required]
    public int CityID { get; set; }
    [ForeignKey("CityID")]
    public virtual City CityParent { get; set; }
    //------------------------------------------------------------//
    [MaxLength(100)]
    [LocalizedAttribute("Address")]
    public string Address { get; set; }
    //------------------------------------------------------------//
    [LocalizedAttribute("PostalCode")]
    public string PostalCode { get; set; }
    //------------------------------------------------------------//
    [MaxLength(255)]
    [LocalizedAttribute("PhotoPath")]
    public string PhotoPath { get; set; }
}
 public class User : Man
{
    [MaxLength(20)]
    [LocalizedAttribute("Username")]
    public string UserName { get; set; }
    //------------------------------------------------------------//
    [DataType(DataType.Password)]
    [MaxLength(100), MinLength(6, ErrorMessageResourceType = typeof(MAHAL_E_MA_Model.Properties.Resources), ErrorMessageResourceName = "ErrorPasswordLength")]
    [LocalizedAttribute("Password")]
    public string Password { get; set; }
    //------------------------------------------------------------//
    [DataType(DataType.Password)]
    [Compare("Password", ErrorMessageResourceType = typeof(MAHAL_E_MA_Model.Properties.Resources), ErrorMessageResourceName = "ErrorConfirmPassword")]
    [LocalizedAttribute("ConfirmPassword")]
    public string ConfirmPassword { get; set; }
    //------------------------------------------------------------//
    [DataType(DataType.EmailAddress, ErrorMessageResourceType = typeof(MAHAL_E_MA_Model.Properties.Resources), ErrorMessageResourceName = "ErrorEmailInvalid")]
    [MaxLength(20)]
    [RegularExpression(@"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+'.[a-zA-Z]{2,}")]
    [LocalizedAttribute("Email")]
    public string Email { get; set; }
    //------------------------------------------------------------//
    [MaxLength(30)]
    [LocalizedAttribute("Title")]
    public string Title { get; set; }
    //------------------------------------------------------------//
    [MaxLength(10)]
    [LocalizedAttribute("HireDate")]
    public int HireDate { get; set; }
    //------------------------------------------------------------//
    [LocalizedAttribute("ReportsTo")]
    public long ReportsTo { get; set; }
    [ForeignKey("ReportsTo")]
    public virtual IList<User> ReportsChild { get; set; }
}
public class City
{
    [Key]
    [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public int CityID { get; set; }
    //------------------------------------------------------------//
    [Required, MaxLength(20)]
    [LocalizedAttribute("Name")]
    public string Name { get; set; }
    //------------------------------------------------------------//
    [LocalizedAttribute("PhoneCode")]
    public int PhoneCode { get; set; }
    //------------------------------------------------------------//
    [Required, MaxLength(10)]
    public int ModifiedDate { get; set; }
}
public class CityUser
{
    [Key]
    [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public int CityUserID { get; set; }
    //------------------------------------------------------------//
    [Required]
    public long ModifiedByUserID { get; set; }
    [ForeignKey("ModifiedByUserID")]
    public virtual User OperatorUser { get; set; }
    //------------------------------------------------------------//
    [Required]
    public int CityID { get; set; }
    [ForeignKey("CityID")]
    public virtual City City { get; set; }
}

但是当EF5开始创建数据库时，前面提到的错误出现了!!我能做些什么呢?我读了很多博客，对数据模型做了一些修改。但仍然无法摆脱这个错误....顺便说一下，我想使用DataAnnotations来声明关系。

现在有没有人能帮我摆脱这个问题??!!!!(

认为,

modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();