C# 实体框架代码优先，迁移错误

我的asp.net mvc应用程序中有4个模型，在编写Update Database命令时出错

在表“约会”上引入外键约束“FK_dbo.Appointments_dbo.DoctorId”可能会导致循环或多个级联路径。指定“在删除时不执行操作”或“在更新时不执行操作”，或修改其他外键约束。 无法创建约束或索引。请参阅前面的错误

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问题出在哪里？

看看这个，看看它是否有帮助：

public class Appointment
{
    public Appointment()
    {
        Status = "UnCompleted";
    }

    [Display(Name = "Appointment Id")]
    [Key]
    public int AppoiId { get; set; }

    [Display(Name = "Patient Id")]
    public int PatientId { get; set; }
    [ForeignKey("PatientId")]
    public virtual Patient Patient { get; set; }

    [Display(Name = "Clinic Id")]
    public int ClinicId { get; set; }
    [ForeignKey("ClinicId")]
    public virtual Clinic Clinic { get; set; }

    [Display(Name = "Doctor Id")]
    public int DoctorId { get; set; }
    [ForeignKey("DoctorId")]
    public virtual Doctor Doctor { get; set; }

    [Required]
    [DataType(DataType.Date)]
    public string Date { get; set; }
    [Required]
    [DataType(DataType.Time)]
    public string Time { get; set; }
    public string Status { get; set; }
}`public class Doctor
{

    [Display(Name = "Doctor Id")]
    [Key]
    public int DoctorId { get; set; }
    [Required(ErrorMessage ="Please Enter First Name")]
    [Display(Name ="First Name")]
    public string FirstName { get; set; }
    [Required(ErrorMessage = "Please Enter Last Name")]
    [Display(Name = "Last Name")]
    public string LastName { get; set; }
    [Required(ErrorMessage ="Please Enter Email")]
    [EmailAddress]
    public string Email { get; set; }
    [Required(ErrorMessage ="Please Enter Password")]
    [Display(Name ="Password")]
    [DataType(DataType.Password)]
    [NotMapped]
    public string Password { get; set; }
    [Required(ErrorMessage = "Please Enter Phone number")]
    [Display(Name ="Phone")]
    public string Phone { get; set; }
    public int ClinicId { get; set; }
    [ForeignKey("ClinicId")]
    public virtual Clinic Clinic { get; set; }
}`public class Clinic
{
    [Key]
    [Display(Name = "Clinic Id")]
    public int ClinicId { get; set; }
    [Required(ErrorMessage ="Please Enter Clinic Name")]
    [Display(Name = "Clinic Name")]
    public string ClinicName { get; set; }
    [Display(Name ="No. of Doctors")]
    public int No_Doctors { get; set; }
    [Required]
    [Display(Name ="Available Time")]
    public string Available_time { get; set; }

}`public class Report
{
    [Key]
    public int ReportId { get; set; }

    public int AppoiId { get; set; }
    [ForeignKey("AppoiId")]
    public virtual Appointment Appointment { get; set; }

    public int PatientId { get; set; }
    [ForeignKey("PatientId")]
    public virtual Patient Patient { get; set; }

    public int DoctorId { get; set; }
    [ForeignKey("DoctorId")]
    public virtual Doctor Doctor { get; set; }

    [Required]
    public string Symptoms { get; set; }
    [Required]
    public string Diagnosis { get; set; }
    public string Date { get; set; }
    [Required]
    [Display(Name ="Report Type")]
    public Type ReportType { get; set; }
}`