Что имеем: 3 класса

  TStaffs = class(TObject)
  private
    FidstStaff: integer;
    FStaffName: Ansistring;
    procedure SetIdstStaff(aValue: integer);
    procedure SetStaffName(const aValue: Ansistring);
  public
    constructor Create(aIdstStaff: integer; const aStaffName: Ansistring);
    destructor Destroy;override;
    property idstStaff: integer read FidstStaff write SetIdstStaff;
    property StaffName: Ansistring read FStaffName write SetStaffName;
  end;

  TDepartmentData = class(TObject)
  private
    FidstDepartment: Integer;
    FidstRank: integer;
    FStaffsList: TList;
  protected
    function GetStaffs(aIndex: integer): TStaffs;virtual;
    function GetStaffsCount: integer;virtual;
  public
    constructor Create(aIdstDepartment: integer; aIdstRank: integer);
    destructor Destroy;override;
    function AddStaff(aIdstStaff: integer; const aStaffName: Ansistring): integer;
    property idstDepartment: integer read FidstDepartment write FidstDepartment;
    property idstRank: integer read FidstRank write FidstRank;
    property Staffs[aIndex: integer]: TStaffs read GetStaffs;
    property StaffsCount: integer read GetStaffsCount;
  end;

  TDepartment = class(TObject)
  private
    FDepartmentData: TList;
  protected
    function GetDepartment(aIndex: integer): TDepartmentData;virtual;
    function GetDepartmentCount: integer;virtual;
  public
    constructor Create();
    destructor Destroy;override;
    function AddDepartment(aIdstDepartment: integer; aIdstRank: integer): integer;
    property Department[aIndex: integer]: TDepartmentData read GetDepartment;
    property DepartmentCount: integer read GetDepartmentCount;
  end;

Вопрос: как из TDepartment добавлять Staff'ов в TDepartmentData?