I make use of the Mydac components by devart (corelab) to access MySql from Delphi (2006)
Very often I need to work with data in a TClientDataSet
What is the best way to convert the dataset of a TMyQuery to TClientDataSet
Currently I am using
var
MyQuery : TMyQuery;
Dsp : TDataSetProvider;
Cds : TClientDataSet;
begin
MyQuery := nil;
Dsp := nil;
Cds := nil;
try
MyQuery := TMyQuery.Create(nil);
Dsp := TDataSetProvider.Create(nil);
Cds := TClientDataSet.Create(nil);
MyQuery.Connection := TheConnection;
MyQuery.SQL.Text := CmdStr;
Dsp.DataSet := MyQuery;
Cds.SetProvider(Dsp);
Cds.Open;
////////////////////////////////////////////////////////////////////////
/// MAKE USES OF THE CDS //
////////////////////////////////////////////////////////////////////////
finally
FreeAndNil(Cds);
FreeAndNil(Dsp);
FreeAndNil(MyQuery);
end;
end;
Is there a better way of doing this ?
If you really do need this very often, then make it a function, like so:
function CreateAndOpenClientDataset(AOwner: TComponent;
AConnection: TConnection; ACommand: string): TClientDataSet;
var
MyQuery: TMyQuery;
Dsp: TDataSetProvider;
begin
Result := TClientDataSet.Create(AOwner);
try
MyQuery := TMyQuery.Create(Result);
MyQuery.Connection := AConnection;
MyQuery.SQL.Text := ACommand;
Dsp := TDataSetProvider.Create(Result);
Dsp.DataSet := MyQuery;
Result.SetProvider(Dsp);
Result.Open;
except
Result.Free;
raise;
end;
end;
This function you can use in all places instead of TClientDataSet.Create(), and unless an exception is raised you will be given an open TClientDataSet which owns and that way also frees the two helper objects.
(Note: I only use the DevArt components for MS Sql Server, so I can't test. The code may well contain errors, but the general idea works.)
Related
With a dynamically created TFDQuery,TClientDataSet, and TDataSetProvider I bump into the "Missing data provider or data packet" with this code:
procedure ResetSavedPasswords(ADataModuleDataBaseAdmin : TDataModuleDataBaseAdmin);
var
lQuery : TFDQuery;
lCDS : TClientDataSet;
lProvider : TDataSetProvider;
begin
lFrmBezig := TFormBezig.Create(nil);
lQuery := TFDQuery.Create(nil);
lProvider := TDataSetProvider.Create(Application);
lCDS := TClientDataSet.Create(nil);
try
lQuery.Connection := ADataModuleDataBaseAdmin.FDConnectionTimeTell;
lQuery.CachedUpdates := true;
lProvider.Options := lProvider.Options - [poUseQuoteChar];
lProvider.DataSet := lQuery;
lProvider.Name := 'prvResetSavedPW';
lCDS.ProviderName := lProvider.Name;
lQuery.SQL.Text := Format('select %s,%s from <owner>%s',[sMedMedID,sMedSavedPassword,SMedTabelNaam]),ADataModuleDataBaseAdmin;
lCDS.Open;
Note that the created TDataSetProvider has an owner, based on this answer:
If DatasetProvider has no owner, ClientDataSet can not obtain a reference to the provider
But I still get the error. Opening the TFDQuery first shows me it has data.
What can be the reason?
Using FireDAC with Delphi 10.4. Sydney in a Win32 app.
It turns out that TClientDataSet needs an owner too:
lCDS := TClientDataSet.Create(Application);
This is obvious from the code that triggered the exception:
function TCustomClientDataSet.GetAppServer: IAppServer;
var
ProvComp: TComponent;
DS: TObject;
begin
if not HasAppServer then
begin
if ProviderName <> '' then
if Assigned(RemoteServer) then
FAppServer := RemoteServer.GetServer
else if Assigned(ConnectionBroker) then
FAppServer := ConnectionBroker.GetServer
else
begin
if Assigned(Owner) then
begin
ProvComp := Owner.FindComponent(ProviderName);
if Assigned(ProvComp) and (ProvComp is TCustomProvider) then
begin
DS := GetObjectProperty(ProvComp, 'DataSet');
if Assigned(DS) and (DS = Self) then
DatabaseError(SNoCircularReference, Self);
FAppServer := TLocalAppServer.Create(TCustomProvider(ProvComp));
end;
end;
end;
if not HasAppServer then
DatabaseError(SNoDataProvider, Self);
end;
Result := FAppServer;
end;
The Assigned(Owner) fails, so the code does not bother looking for the TDataSetProvider
I am working on a legacy code which contains some TQuery components. I was trying to create a function which convert the TQuery Parameters into TParameters so that i can assign them into the Parameters property of an ADO Component (Like ADOQuery or ADODataSet).
I tried the following which i got from internet.
function ConvertToADOParms(Owner: TADODataset; aParams: TParams): TParameters;
var i: integer;
begin
// Convert a standard TParams object to an ADO-specific TParameters object
Result :=nil;
try
if aParams = nil then exit;
Result :=TParameters.create( Owner, TParameter);
for i:=0 to aParams.count - 1 do
begin
if aParams[i] = nil then continue;
with Result.AddParameter do
begin
Name := aParams[i].Name;
Datatype :=aParams[i].DataType;
Direction :=TParameterDirection(aParams[i].ParamType);
Size :=aParams[i].size;
Value :=aParams[i].value;
end;
end;
except
on e:exception do
begin
Result :=nil;
showmessage('Could not convert standard parameter object to ADO parameter object: '+e.message);
end;
end;
end;
But i am getting Invalid Class Typecast Error. When i debug the code i found that the error occurs at this function in ADODB unit
function TParameters.GetCommand: TADOCommand;
begin
Result := GetOwner as TADOCommand;
end;
Help Please. I am Using Delphi 5
I don't make much sense of the function prototype. It requests an owner for the collection that is returned by the function and as such should IMHO be independent.
I would simply get rid of that and operate directly with the passed ADO object. For example:
procedure FillParamsADO(Params: TParams; Dataset: TADODataset);
var
i: Integer;
begin
Dataset.Parameters.Clear;
for i := 0 to Params.Count-1 do
begin
with Dataset.Parameters.AddParameter do
begin
Name := Params[i].Name;
DataType := Params[i].DataType;
Direction := TParameterDirection(Params[i].ParamType);
Size := Params[i].Size;
Value := Params[i].Value;
end;
end;
end;
I need to use a TRichEdit at runtime to perform the rtf to text conversion as discussed here. I succeded in doing this but I had to set a dummy form as parent if not I cannot populate the TRichedit.Lines. (Error: parent is missing).
I paste my funciton below, can anyone suggest a way to avoid to define a parent? Can you also comment on this and tell me if you find a more performant idea?
Note: I need a string, not TStrings as output, this is why it has been designed like this.
function RtfToText(const RTF: string;ReplaceLineFeedWithSpace: Boolean): string;
var
RTFConverter: TRichEdit;
MyStringStream: TStringStream;
i: integer;
CustomLineFeed: string;
begin
if ReplaceLineFeedWithSpace then
CustomLineFeed := ' '
else
CustomLineFeed := #13;
try
RTFConverter := TRichEdit.Create(nil);
try
MyStringStream := TStringStream.Create(RTF);
RTFConverter.parent := Form4; // this is the part I don't like
RTFConverter.Lines.LoadFromStream(MyStringStream);
RTFConverter.PlainText := True;
for i := 0 to RTFConverter.Lines.Count - 1 do
begin
if i < RTFConverter.Lines.Count - 1 then
Result := Result + RTFConverter.Lines[i] + CustomLineFeed
else
Result := Result + RTFConverter.Lines[i];
end;
finally
MyStringStream.Free;
end;
finally
RTFConverter.Free;
end;
end;
UPDATE:
After the answer I updated the function and write it here for reference:
function RtfToText(const RTF: string;ReplaceLineFeedWithSpace: Boolean): string;
var
RTFConverter: TRichEdit;
MyStringStream: TStringStream;
begin
RTFConverter := TRichEdit.CreateParented(HWND_MESSAGE);
try
MyStringStream := TStringStream.Create(RTF);
try
RTFConverter.Lines.LoadFromStream(MyStringStream);
RTFConverter.PlainText := True;
RTFConverter.Lines.StrictDelimiter := True;
if ReplaceLineFeedWithSpace then
RTFConverter.Lines.Delimiter := ' '
else
RTFConverter.Lines.Delimiter := #13;
Result := RTFConverter.Lines.DelimitedText;
finally
MyStringStream.Free;
end;
finally
RTFConverter.Free;
end;
end;
TRichEdit control is an wrapper around the RichEdit control in Windows. Windows's controls are... well.. Windows, and they need an Window Handle to work. Delphi needs to call CreateWindow or CreateWindowEx to create the Handle, and both routines need an valid parent Window Handle to work. Delphi tries to use the handle of the control's parent (and it makes sense!). Happily one can use an alternative constructor (the CreateParanted(HWND) constructor) and the nice people at Microsoft made up the HWND_MESSAGE to be used as parent for windows that don't actually need a "window" (messaging-only).
This code works as expected:
procedure TForm2.Button2Click(Sender: TObject);
var R:TRichEdit;
L:TStringList;
begin
R := TRichEdit.CreateParented(HWND_MESSAGE);
try
R.PlainText := False;
R.Lines.LoadFromFile('C:\Temp\text.rtf');
R.PlainText := True;
Memo1.Lines.Text := R.Lines.Text;
finally
R.Free;
end;
end;
This is part of the way the VCL works, and you're not going to get it to work differently without some heavy workarounds. But you don't need to define a dummy form to be the parent; just use your current form and set visible := false; on the TRichEdit.
If you really want to improve performance, though, you could throw out that loop you're using to build a result string. It has to reallocate and copy memory a lot. Use the Text property of TrichEdit.Lines to get a CRLF between each line, and DelimitedText to get somethimg else, such as spaces. They use an internal buffer that's only allocated once, which will speed up the concatenation quite a bit if you're working with a lot of text.
I use DrawRichText to draw RTF without a RichEdit control. (IIRC this is called Windowless Rich Edit Controls.) Maybe you can use this also for converting - however I have never tried this.
This has been the most helpfull for me to get started with TRichEdit, but not with the conversion. This however works as expected and you don't need to set the Line Delimiter:
// RTF to Plain:
procedure TForm3.Button1Click(Sender: TObject);
var
l:TStringList;
s:WideString;
RE:TRichEdit;
ss:TStringStream;
begin
ss := TStringStream.Create;
s := Memo1.Text; // Input String
RE := TRichEdit.CreateParented(HWND_MESSAGE);
l := TStringList.Create;
l.Add(s);
ss.Position := 0;
l.SaveToStream(ss);
ss.Position := 0;
RE.Lines.LoadFromStream(ss);
Memo2.Text := RE.Text; // Output String
end;
// Plain to RTF:
procedure TForm3.Button2Click(Sender: TObject);
var
RE:TRichEdit;
ss:TStringStream;
begin
RE := TRichEdit.CreateParented(HWND_MESSAGE);
RE.Text := Memo2.Text; // Input String
ss := TStringStream.Create;
ss.Position := 0;
RE.Lines.SaveToStream(ss);
ss.Position := 0;
Memo1.Text := ss.ReadString(ss.Size); // Output String
end;
I'm using the TStringList "l" in the conversion to plain because somehow the TStringStream puts every single character in a new line.
Edit: Made the code a bit nicer and removed unused variables.
I need to use a TRichEdit at runtime to perform the rtf to text conversion as discussed here. I succeded in doing this but I had to set a dummy form as parent if not I cannot populate the TRichedit.Lines. (Error: parent is missing).
I paste my funciton below, can anyone suggest a way to avoid to define a parent? Can you also comment on this and tell me if you find a more performant idea?
Note: I need a string, not TStrings as output, this is why it has been designed like this.
function RtfToText(const RTF: string;ReplaceLineFeedWithSpace: Boolean): string;
var
RTFConverter: TRichEdit;
MyStringStream: TStringStream;
i: integer;
CustomLineFeed: string;
begin
if ReplaceLineFeedWithSpace then
CustomLineFeed := ' '
else
CustomLineFeed := #13;
try
RTFConverter := TRichEdit.Create(nil);
try
MyStringStream := TStringStream.Create(RTF);
RTFConverter.parent := Form4; // this is the part I don't like
RTFConverter.Lines.LoadFromStream(MyStringStream);
RTFConverter.PlainText := True;
for i := 0 to RTFConverter.Lines.Count - 1 do
begin
if i < RTFConverter.Lines.Count - 1 then
Result := Result + RTFConverter.Lines[i] + CustomLineFeed
else
Result := Result + RTFConverter.Lines[i];
end;
finally
MyStringStream.Free;
end;
finally
RTFConverter.Free;
end;
end;
UPDATE:
After the answer I updated the function and write it here for reference:
function RtfToText(const RTF: string;ReplaceLineFeedWithSpace: Boolean): string;
var
RTFConverter: TRichEdit;
MyStringStream: TStringStream;
begin
RTFConverter := TRichEdit.CreateParented(HWND_MESSAGE);
try
MyStringStream := TStringStream.Create(RTF);
try
RTFConverter.Lines.LoadFromStream(MyStringStream);
RTFConverter.PlainText := True;
RTFConverter.Lines.StrictDelimiter := True;
if ReplaceLineFeedWithSpace then
RTFConverter.Lines.Delimiter := ' '
else
RTFConverter.Lines.Delimiter := #13;
Result := RTFConverter.Lines.DelimitedText;
finally
MyStringStream.Free;
end;
finally
RTFConverter.Free;
end;
end;
TRichEdit control is an wrapper around the RichEdit control in Windows. Windows's controls are... well.. Windows, and they need an Window Handle to work. Delphi needs to call CreateWindow or CreateWindowEx to create the Handle, and both routines need an valid parent Window Handle to work. Delphi tries to use the handle of the control's parent (and it makes sense!). Happily one can use an alternative constructor (the CreateParanted(HWND) constructor) and the nice people at Microsoft made up the HWND_MESSAGE to be used as parent for windows that don't actually need a "window" (messaging-only).
This code works as expected:
procedure TForm2.Button2Click(Sender: TObject);
var R:TRichEdit;
L:TStringList;
begin
R := TRichEdit.CreateParented(HWND_MESSAGE);
try
R.PlainText := False;
R.Lines.LoadFromFile('C:\Temp\text.rtf');
R.PlainText := True;
Memo1.Lines.Text := R.Lines.Text;
finally
R.Free;
end;
end;
This is part of the way the VCL works, and you're not going to get it to work differently without some heavy workarounds. But you don't need to define a dummy form to be the parent; just use your current form and set visible := false; on the TRichEdit.
If you really want to improve performance, though, you could throw out that loop you're using to build a result string. It has to reallocate and copy memory a lot. Use the Text property of TrichEdit.Lines to get a CRLF between each line, and DelimitedText to get somethimg else, such as spaces. They use an internal buffer that's only allocated once, which will speed up the concatenation quite a bit if you're working with a lot of text.
I use DrawRichText to draw RTF without a RichEdit control. (IIRC this is called Windowless Rich Edit Controls.) Maybe you can use this also for converting - however I have never tried this.
This has been the most helpfull for me to get started with TRichEdit, but not with the conversion. This however works as expected and you don't need to set the Line Delimiter:
// RTF to Plain:
procedure TForm3.Button1Click(Sender: TObject);
var
l:TStringList;
s:WideString;
RE:TRichEdit;
ss:TStringStream;
begin
ss := TStringStream.Create;
s := Memo1.Text; // Input String
RE := TRichEdit.CreateParented(HWND_MESSAGE);
l := TStringList.Create;
l.Add(s);
ss.Position := 0;
l.SaveToStream(ss);
ss.Position := 0;
RE.Lines.LoadFromStream(ss);
Memo2.Text := RE.Text; // Output String
end;
// Plain to RTF:
procedure TForm3.Button2Click(Sender: TObject);
var
RE:TRichEdit;
ss:TStringStream;
begin
RE := TRichEdit.CreateParented(HWND_MESSAGE);
RE.Text := Memo2.Text; // Input String
ss := TStringStream.Create;
ss.Position := 0;
RE.Lines.SaveToStream(ss);
ss.Position := 0;
Memo1.Text := ss.ReadString(ss.Size); // Output String
end;
I'm using the TStringList "l" in the conversion to plain because somehow the TStringStream puts every single character in a new line.
Edit: Made the code a bit nicer and removed unused variables.
Is it possible to, for instance, replace and free a TEdit with a subclassed component instantiated (conditionally) at runtime? If so, how and when it should be done? I've tried to set the parent to nil and to call free() in the form constructor and AfterConstruction methods but in both cases I got a runtime error.
Being more specific, I got an Access violation error (EAccessViolation). It seems François is right when he says that freeing components at frame costruction messes with Form controls housekeeping.
This more generic routine works either with a Form or Frame (updated to use a subclass for the new control):
function ReplaceControlEx(AControl: TControl; const AControlClass: TControlClass; const ANewName: string; const IsFreed : Boolean = True): TControl;
begin
if AControl = nil then
begin
Result := nil;
Exit;
end;
Result := AControlClass.Create(AControl.Owner);
CloneProperties(AControl, Result);// copy all properties to new control
// Result.Left := AControl.Left; // or copy some properties manually...
// Result.Top := AControl.Top;
Result.Name := ANewName;
Result.Parent := AControl.Parent; // needed for the InsertControl & RemoveControl magic
if IsFreed then
FreeAndNil(AControl);
end;
function ReplaceControl(AControl: TControl; const ANewName: string; const IsFreed : Boolean = True): TControl;
begin
if AControl = nil then
Result := nil
else
Result := ReplaceControlEx(AControl, TControlClass(AControl.ClassType), ANewName, IsFreed);
end;
using this routine to pass the properties to the new control
procedure CloneProperties(const Source: TControl; const Dest: TControl);
var
ms: TMemoryStream;
OldName: string;
begin
OldName := Source.Name;
Source.Name := ''; // needed to avoid Name collision
try
ms := TMemoryStream.Create;
try
ms.WriteComponent(Source);
ms.Position := 0;
ms.ReadComponent(Dest);
finally
ms.Free;
end;
finally
Source.Name := OldName;
end;
end;
use it like:
procedure TFrame1.AfterConstruction;
var
I: Integer;
NewEdit: TMyEdit;
begin
inherited;
NewEdit := ReplaceControlEx(Edit1, TMyEdit, 'Edit2') as TMyEdit;
if Assigned(NewEdit) then
begin
NewEdit.Text := 'My Brand New Edit';
NewEdit.Author := 'Myself';
end;
for I:=0 to ControlCount-1 do
begin
ShowMessage(Controls[I].Name);
end;
end;
CAUTION: If you are doing this inside the AfterConstruction of the Frame, beware that the hosting Form construction is not finished yet.
Freeing Controls there, might cause a lot of problems as you're messing up with Form controls housekeeping.
See what you get if you try to read the new Edit Caption to display in the ShowMessage...
In that case you would want to use
...ReplaceControl(Edit1, 'Edit2', False)
and then do a
...FreeAndNil(Edit1)
later.
You have to call RemoveControl of the TEdit's parent to remove the control. Use InsertControl to add the new control.
var Edit2: TEdit;
begin
Edit2 := TEdit.Create(self);
Edit2.Left := Edit1.Left;
Edit2.Top := Edit2.Top;
Edit1.Parent.Insertcontrol(Edit2);
TWinControl(Edit1.parent).RemoveControl(Edit1);
Edit1.Free;
end;
Replace TEdit.Create to the class you want to use, and copy all properties you need like I did with Left and Top.
You can actually use RTTI (look in the TypInfo unit) to clone all the matching properties. I wrote code for this a while back, but I can't find it now. I'll keep looking.