Aggregate of multiple UI controls bound to one database column - database

Question

I currently have a TDBRadioGroup bound to a CHAR column on the database using the Values property to specify the value stored in the database column for each radio button. Now we have a requirement to add 2 new radio groups along side the existing one that would modify the value. In other words I basically need 3 controls on the form to act as one in a data-aware configuration for the purposes of determining the value stored. A simple example might be if each radio group has a one-character value, and in the database you concatenate them into a 3-character string. Our mapping is more complex than that but that's the general idea. What would be a good way to do this? If someone tells me live bindings would be the way to go, that would be good to know, as it would be help me to convince management to upgrade Delphi. We're stuck on XE.

Answer 1

Interesting q!
I hope I've understood you correctly. Suppose there is a form with 3 radiogroups, one per line, like so
*A B C
D *E F
G H *I
where the asterisks indicates the positions of the selected buttons and suppose
that these settings translate into a field value AEI in a row of a dataset.
If the G entry of the 3rd RG is clicked, the dataset field value should become
GEI. That's what I've assumed you are looking for.
The code below is a "proof of concept" which implements the above functionality.
It does so using 3 standard (non-db-aware) TRadioGroups and an adaptor class
TDBRadioGroupAdaptor which makes these operate as db-aware RadioGroups. The
TDBRadioGroupAdaptor uses a descendant, TRGFieldDataLink, of the standard TFieldDataLink (see DBCtrls.Pas)
to interface with the dataset. I've used a TClientDataSet so the project can be completely
self-contained and I've avoided the use of generices as you didn't specify a Delphi version.
Most of the db-aware functionality is contained in the TRGFieldDataLink, which
serves to interface the dataset and the RadioGroups and differs from a standard
TFieldDataLink in that it treats the field value as composed of N (3 in the code example but it supports an arbitrary number)
sub-fields which each have their own RadioGroup. As ever with implementing db-aware
functionality, the code for the TDBRadioGroupAdaptor and TRGFieldDataLink is fairly
long-winded, as most of it is necessary but not very interesting. About the only
ones that are interesting, in that they make the wheels go around, are
function TRGFieldDataLink.GetGroupString : String;
// Returns a string from the ItemIndexes of the RadioGroups
procedure TRGFieldDataLink.GetGroupValues;
// Sets the DataSet field from the RadioGroup ItemIndexes
which I hope are self-explanatory from the embedded comments.
Because it's only supposed to be a proof-of-concept, the implementation is incomplete,
lacking f.i. keyboard support, but that could easily be added by mimicking the
source code of the standard TDBRadioGroup.
Obviously, something similar could be used to treat subfields of a dataset field as
a group of strings independently editable in a group of TEdits.
Also obviously, it would be possible to turn the TDBRadioGroupAdaptor into a full-blown compound component which includes its own radiogroups, but I've left that as an exercise for the reader.
Code (warning: long!)
type
TDBRadioGroupAdaptor = class;
TRGFieldDataLink = class(TFieldDataLink)
private
FAdaptor: TDBRadioGroupAdaptor;
FRecordChanging : Boolean;
procedure GetGroupValues;
function GetGroupString: String;
procedure SetGroupValues(AValue: String);
public
constructor Create(AAdaptor : TDBRadioGroupAdaptor);
destructor Destroy; override;
procedure RecordChanged(Field : TField); override;
procedure UpdateData; override;
property Adaptor : TDBRadioGroupAdaptor read FAdaptor write FAdaptor;
end;
TDBRadioGroupAdaptor = class
private
FDataLink : TRGFieldDataLink;
FRadioGroups : TList;
procedure SetDataSource(Value : TDataSource);
function GetDataSource : TDataSource;
function GetRadioGroup(Index: Integer): TRadioGroup;
procedure ItemClicked(Sender : TObject);
procedure SetFieldName(const Value: string);
function GetFieldName : String;
public
constructor Create;
destructor Destroy; override;
procedure Add(ARadioGroup : TRadioGroup);
property DataSource : TDataSource read GetDataSource write SetDataSource;
property FieldName : string read GetFieldName write SetFieldName;
property RadioGroup[Index : Integer] : TRadioGroup read GetRadioGroup;
end;
type
TForm1 = class(TForm)
DBGrid1: TDBGrid;
ClientDataSet1: TClientDataSet;
DataSource1: TDataSource;
DBNavigator1: TDBNavigator;
Button1: TButton;
RadioGroup1: TRadioGroup;
RadioGroup2: TRadioGroup;
RadioGroup3: TRadioGroup;
DBEdit1: TDBEdit;
DBRadioGroup1: TDBRadioGroup;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
protected
public
Adaptor : TDBRadioGroupAdaptor;
end;
[...]
{ TRGFieldDataLink }
constructor TRGFieldDataLink.Create(AAdaptor : TDBRadioGroupAdaptor);
begin
inherited Create;
Adaptor := AAdaptor;
end;
destructor TRGFieldDataLink.Destroy;
begin
inherited;
end;
procedure TRGFieldDataLink.SetGroupValues(AValue : String);
// Sets the ItemIndexes of the RadioGroups by matching each character of AValue
// to the contents of their Items
var
i,
Index : Integer;
S : String;
begin
if AValue = '' then Exit; // To avoid error when CreateDataSet is called
for i := 0 to Adaptor.FRadioGroups.Count - 1 do begin
S := AValue[i + 1];
Index := Adaptor.RadioGroup[i].Items.IndexOf(S);
Adaptor.RadioGroup[i].ItemIndex := Index;
end;
end;
procedure TRGFieldDataLink.RecordChanged(Field : TField);
// called when the dataset goes to a new record, e.g. during scrolling
// and sets the RadioGroups' ItemIndexes from the dataset data
var
FieldValue : String;
begin
Assert(DataSet <> Nil);
if FRecordChanging then exit; // just in case, avoid re-entrancy
try
FRecordChanging := True;
if Field = Nil then
Field := DataSet.FieldByName(FieldName); // Yukky way of setting Field
FieldValue := Field.AsString;
SetGroupValues(FieldValue);
finally
FRecordChanging := False;
end;
end;
function TRGFieldDataLink.GetGroupString : String;
// Returns a string from the ItemIndexes of the RadioGroups
var
i : Integer;
S : String;
begin
Result := '';
for i := 0 to Adaptor.FRadioGroups.Count - 1 do begin
S := Adaptor.RadioGroup[i].Items[Adaptor.RadioGroup[i].ItemIndex];
Result := Result + S [1];
end;
end;
procedure TRGFieldDataLink.GetGroupValues;
// Sets the DataSet field from the RadioGroup ItemIndexes
var
FieldValue,
S : String;
begin
Assert(DataSet <> Nil);
S := Field.AsString;
FieldValue := GetGroupString;
Field.AsString := FieldValue;
end;
procedure TRGFieldDataLink.UpdateData;
// Called by RTL to update the dataset record from the RadioGroups
begin
GetGroupValues;
end;
{ TDBRadioGroupAdaptor }
procedure TDBRadioGroupAdaptor.Add(ARadioGroup: TRadioGroup);
begin
FRadioGroups.Add(ARadioGroup);
ARadioGroup.OnClick := ItemClicked;
end;
constructor TDBRadioGroupAdaptor.Create;
begin
inherited;
FRadioGroups := TList.Create;
FDataLink := TRGFieldDataLink.Create(Self);
end;
destructor TDBRadioGroupAdaptor.Destroy;
begin
FDataLink.Free;
FRadioGroups.Free;
inherited Destroy;
end;
function TDBRadioGroupAdaptor.GetDataSource: TDataSource;
begin
Result := FDataLink.DataSource;
end;
procedure TDBRadioGroupAdaptor.SetDataSource(Value: TDataSource);
begin
FDataLink.DataSource := Value;
end;
function TDBRadioGroupAdaptor.GetRadioGroup(Index: Integer): TRadioGroup;
begin
Result := TRadioGroup(FRadioGroups[Index]);
end;
procedure TDBRadioGroupAdaptor.ItemClicked(Sender: TObject);
// Responds to one of the RadioGroups being clicked to put the DataSet into Edit state
// and updates the DataSet field from the ItemIndexes of the RadioGroups
var
S : String;
begin
if not FDataLink.FRecordChanging then begin
S := FDataLink.GetGroupString;
FDataLink.Edit;
FDataLink.SetGroupValues(S);
end;
end;
procedure TDBRadioGroupAdaptor.SetFieldName(const Value: string);
begin
FDataLink.FieldName := Value;
end;
function TDBRadioGroupAdaptor.GetFieldName: string;
begin
Result := FDataLink.FieldName;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
Field : TField;
begin
// Create 2 fields in the CDS
Field := TIntegerField.Create(Self);
Field.FieldName := 'ID';
Field.FieldKind := fkData;
Field.DataSet := ClientDataSet1;
Field := TStringField.Create(Self);
Field.FieldName := 'Value';
Field.Size := 40;
Field.FieldKind := fkData;
Field.DataSet := ClientDataSet1;
RadioGroup1.Items.Add('A');
RadioGroup1.Items.Add('B');
RadioGroup1.Items.Add('C');
RadioGroup2.Items.Add('D');
RadioGroup2.Items.Add('E');
RadioGroup2.Items.Add('F');
RadioGroup3.Items.Add('G');
RadioGroup3.Items.Add('H');
RadioGroup3.Items.Add('I');
Adaptor := TDBRadioGroupAdaptor.Create;
Adaptor.Add(RadioGroup1);
Adaptor.Add(RadioGroup2);
Adaptor.Add(RadioGroup3);
Adaptor.DataSource := DataSource1;
Adaptor.FieldName := 'Value';
// Next, set up the CDS
ClientDataSet1.CreateDataSet;
ClientDataSet1.InsertRecord([1, 'AEI']);
ClientDataSet1.InsertRecord([2, 'BDG']);
ClientDataSet1.InsertRecord([3, 'ADG']);
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
Adaptor.Free;
end;