public class Company
{
    [Key]
    public int id { get; set; }
    public string name { get; set; }
    public string sys_id { get; set; }
}

public class Ticket
{
    [Key]
    public int id { get; set; }
    public string company_id { get; set; }
    public string short_desc { get; set; }
}

public class Company
{
    [Key]
    public int id { get; set; }
    public string name { get; set; }
    public string sys_id { get; set; }

    [InverseProperty("company_id")]
    [ForeignKey("sys_id")]
    public virtual ICollection<Ticket> Tickets { get; set; }
}

public class Ticket
{
    [Key]
    public int id { get; set; }
    public string company_id { get; set; }
    public string short_desc { get; set; }

    public virtual Company Company { get; set; }
}

public class Company
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int id { get; set; }

    public string name { get; set; }

    [Key, StringLength(128)]
    public string sys_id { get; set; }
}

public class Ticket
{
    public int id { get; set; }

    public string short_desc { get; set; }

    public string company_id { get; set; }
    [ForeignKey("company_id"), StringLength(128)]
    public virtual Company Company { get; set; }
}