I have created two tabled called Customer and destination . CustomerCode is a primary key in Customer and Foreign key is Destination .when i delete a customer the destination will be deleted.
public class tblCustomerDetails
{
    [Key]
    public string CustomerCode { get; set; }
    public string CustomerName { get; set; }
}
public class tblDestinationDetails
{
    [Key]
    public string DestinationCode { get; set; }
    [ForeignKey("tblCustomerDetails")]
    public string CustomerCode { get; set; }
    public tblCustomerDetails tblCustomerDetails { get; set; }
    public string DestinationName { get; set; }
}
public class tblOrderDetails
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int SrNo { get; set; }
    public int OrderNo { get; set; }
    [ForeignKey("tblCustomerDetails")]
    public string CustomerCode { get; set; }
    public tblCustomerDetails tblCustomerDetails { get; set; }
    [ForeignKey("tblDestinationDetails")]
    public string DestinationCode { get; set; }
    public tblDestinationDetails tblDestinationDetails { get; set; }
}