Ошибка цикличности модели БД

    public abstract class Client
        {
            public int ClientId { get; set; }
     
            [Required(ErrorMessage = "Name is required for Client")]
            public string ClientName { get; set; }
     
            [Required(ErrorMessage = "Phone number is required for Client")]
            public string ClientPhoneNumber { get; set; }
     
            public string Email { get; set; }
     
            public string Comment { get; set; }
     
            [Required(ErrorMessage = "Client should be enabled or disabled")]
            public bool IsDisabled { get; set; }
        }

    public class PrivatePerson : Client // дядя Вася
        {
            public string PrivatePersonSurname { get; set; }
        }

        public class Firm : Client
        {
            [Required(ErrorMessage = "Ownership is required for Firm")]
            public virtual Ownership Ownership { get; set; }
     
            [Required(ErrorMessage = "Client address is required for Firm")]
            public virtual ClientAddress FirmAddress { get; set; }
        }

        public class AdvertisingAgency : Client
        {
            [Required(ErrorMessage = "Ownership is required for Advertising agency")]
            public virtual Ownership Ownership { get; set; }
     
            [Required(ErrorMessage = "Client address is required for Advertising agency")]
            public virtual ClientAddress AdvertisingAgencyAddress { get; set; }
        }

        public class ClientAddress
        {
            public int ClientAddressId { get; set; }
     
            [Required(ErrorMessage = "Postal code is required for Client Address")]
            public int PostalCode { get; set; }
     
            [Required(ErrorMessage = "City is required for Client Address")]
            public virtual City ClientCity { get; set; }
     
            public int POBox { get; set; }
     
            public virtual Street ClientStreet { get; set; }
     
            public string StreetNumber { get; set; }
     
            public int Appartment { get; set; }
     
            public string ClientAddressComment { get; set; }
        }

    public class FivePlusDBContext : DbContext
    {
        public FivePlusDBContext() : base("name = FivePlus")
        {
        }
 
        public virtual DbSet<City> Cities { get; set; }
        public virtual DbSet<Street> Streets { get; set; }
 
        public virtual DbSet<Client> Clients { get; set; }
        public virtual DbSet<ClientAddress> ClientAddresses { get; set; }
 
        public virtual DbSet<Ownership> Ownerships { get; set; }
    }

using (var ctx = new FivePlusDBContext())
            {
                City C_1 = new City() { CityName = "Имя" };
                ctx.Cities.Add(C_1);
                ctx.SaveChanges();
            }