Программная настройка MasterSource и MasterFields

procedure TForm1.ComboBox2Change(Sender: TObject);
begin
if ComboBox2.ItemIndex = 0 then
DBGrid2.DataSource := fDM.DSTovarMainData;
if ComboBox2.ItemIndex = 1 then begin
fDM.TPokupatelData.MasterFields:='IDPokupatela';
DBGrid2.DataSource := fDM.DSPokupatelData;
end;
.......здесь ошибка........
if ComboBox2.ItemIndex = 2 then begin //otchet
if DBGrid1.DataSource = fDM.DSPokupatelData then begin
fDM.TotchetData.MasterFields:='IDPokupatelia';
fDM.TotchetData.MasterSource:=fDM.DSPokupatelData;
end;
if DBGrid1.DataSource = fDM.DSTovarMainData then begin
fDM.TotchetData.MasterSource:=fDM.DSTovarMainData;
fDM.TotchetData.MasterFields:='IdTovara';
end;
DBGrid2.DataSource := fDM.DSotchetData;
end;
.......здесь ошибка........
if ComboBox2.ItemIndex = 3 then begin
fDM.TckladData.MasterFields:='IdTovara';
DBGrid2.DataSource := fDM.DSckladData;
end; end;

if (ComboBox2.ItemIndex = 2) and (DBGrid1.DataSource=fDM.DSTovarMainData) then begin
fDM.TotchetData.MasterFields:='IdTovara';
fDM.TotchetData.MasterSource:=fDM.DSTovarMainData;
DBGrid2.DataSource := fDM.DSotchetData;
end;
if (ComboBox2.ItemIndex = 2) and (DBGrid1.DataSource=fDM.DSPokupatelData) then begin
fDM.TotchetData.MasterFields:='IDPokupatelia';
fDM.TotchetData.MasterSource:=fDM.DSPokupatelData;
DBGrid2.DataSource := fDM.DSotchetData;
end;