Make Non-Windowed Component Data Aware - database

Question

I have a non-windowed component with a date property. I would like to make this component data aware with read and write capabilities to a date field. (In other words, if I change the date at runtime, I would like to write the new date property value to the dataset.) I have googled for examples, but I haven't been able to find any. Found several read-only examples, e.g., TDbLabel, but none that allow changes to be written to the dataset. If anyone can point me to an example, I would be grateful.

Answer 1

Here is a generic code approach to your question
unit Unit1;
interface
uses
Classes
,DB
,DBCtrls
;
type
TDataAwareComponent = class(TComponent)
private
{ private declarations }
FDataLink : TFieldDataLink;
FFromDateChange : Boolean;
function GetDataField: string;
function GetDataSource: TDataSource;
function GetField: TField;
function GetReadOnly: Boolean;
procedure SetDataField(const Value: string);
procedure SetDataSource(const Value: TDataSource);
procedure SetReadOnly(const Value: Boolean);
function GetDateProperty: TDateTime;
procedure SetDateProperty(const Value: TDateTime);
protected
{ protected declarations }
procedure DataChange(Sender : TObject);
public
{ public declarations }
constructor Create(AOwner : TComponent);override;
destructor Destroy;override;
public
property Field : TField read GetField;
property DateProperty : TDateTime read GetDateProperty write SetDateProperty;
published
{ published declarations }
property DataSource : TDataSource read GetDataSource write SetDataSource;
property DataField : string read GetDataField write SetDataField;
property ReadOnly : Boolean read GetReadOnly write SetReadOnly;
end;
implementation
{ TDataAwareComponent }
{------------------------------------------------------------------------------}
constructor TDataAwareComponent.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FDataLink := TFieldDataLink.Create;
FDataLink.Control := Self;
FDataLink.OnDataChange := DataChange;
end;
{------------------------------------------------------------------------------}
destructor TDataAwareComponent.Destroy;
begin
FDataLink.Free;
FDataLink := nil;
inherited;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.DataChange(Sender: TObject);
begin
// Here a visual object would display the underlying field value.
// For example if this component was a TEdit
// the code would be something like
{ if FDataLink.Active then
Self.Text := Field.AsString;
And on the exit event of the TEdit the code would be reversed
so the field can take the value the user entered.
Since you do not need any UI interaction propably this event
is useless to you.
}
// Of course there are more issues you should cover to
// have a complete working solution.
// This is only demostration code.
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetDataField: string;
begin
Result := FDataLink.FieldName
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetDataSource: TDataSource;
begin
Result := FDataLink.DataSource;
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetDateProperty: TDateTime;
begin
//You do not need a separate property since you can access directly the field value.
Result := 0;
if Assigned(Field) and (Field.DataType in [ftTime,ftDate,ftDateTime] then
Result := Field.AsDateTime;
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetField: TField;
begin
Result : FDataLink.Field;
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetReadOnly: Boolean;
begin
Result := FDataLink.ReadOnly;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetDataField(const Value: string);
begin
FDataLink.FieldName := Value;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetDataSource(const Value: TDataSource);
begin
FDataLink.DataSource := Value;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetDateProperty(const Value: TDateTime);
begin
if Assigned(Field) then
begin
FFromDateChange := True;
try
Field.DataSet.Edit;
Field.Value := Value;
finally
FFromDateChange := False;
end;
end;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetReadOnly(const Value: Boolean);
begin
FDataLink.ReadOnly := Value;
end;
{------------------------------------------------------------------------------}
end.

Answer 2

It'd be a bit of code, but if your component has events triggered when its value changes, then that could be used to send updated values to the dataset, if it's in the dsEdit state. You'd also need to handle the various TDataSource Events to know when the dataset is changing.