Copy database to tethered client - delphi

Question

I have created a tethered app. The server needs to copy a Sqlite db
and stream it to the client.
I get the db with this code:
procedure TfmxServer.actStreamTheDbExecute(Sender: TObject);
var
ms: TMemoryStream;
begin
ms := tmemorystream.Create;
ms := dmplanner.GetDbAsStream; // get it from the datamodule
ms.Position := 0;
thrprofServer.SendStream(thrmanServer.RemoteProfiles.First,
'Stream_TheDB', ms); // send it to the client
end;
function TdmPlanner.GetDbAsStream: TMemoryStream; // datamodule
var
fs: TFilestream;
ms: TMemoryStream;
begin
fs := tfilestream.Create(consqlite.Params.Values['Database'] , fmOpenRead);
ms := tmemorystream.Create;
try
ms.loadfromstream(fs); // ms.size = 315392, file size = (315,392 bytes
result := ms; // so I am getting the full db3 file.
result.Position := 0;
finally
freeandnil(fs);
freeandnil(ms); // does this kill the result?
end;
end;
I catch the stream and to write the db with this code:
procedure TfrmMobile_Client_Main.DoStreamTheDb(
const Aresource: TremoteResource);
var
fs: TFilestream;
ms: TMemoryStream;
begin
fs := tfilestream.Create
(dmplannerclient.consqlite.Params.Values['Database'] ,
fmopenreadwrite or fmCreate);
try
ms := TMemoryStream.Create;
ms := TMemoryStream(AResource.Value.AsStream);
ms.Position := 0; // ms.size = 315392, so I got the whole file.
ms.SaveToStream(fs);
dmPlannerClient.FillLbx(lbxRecipeNames);
// now fill a listbox, but when I open a query, I get
// [FireDAC][Phys][SQLite] ERROR: unable to open database file.
finally
freeandnil(fs);
freeandnil(ms);
end;
end;
So my question is, How do I copy the db to the client
and then use it on the client?
Better yet, How do I an in-memory db instead of an on-disk db?
I have tried setting the FDConnection filename to :memory: but that
did not work.
Delphi CE Rio 10.3.2
Thanks...Dan'l' +

Answer 1

I don't think there is a way to copy a Sqlite database in its entirety to a tethered
client short of copying the entire database file to the client, because it may contain
numerous tables and other resources like views, stored procs, etc.
However, copying the entire database as a file is actually quite
simple to do. In the client, you can open a table in it using a local FDConnection
and FDQuery.
Server code:
procedure TApp1Form.SendDBAsStream;
var
StreamToSend : TMemoryStream;
const
DBName = 'D:\Delphi\Code\Sqlite\DB1.Sqlite';
begin
StreamToSend := TMemoryStream.Create;
try
StreamToSend.LoadFromFile(DBName);
StreamToSend.Position := 0;
TetheringAppProfile1.Resources.FindByName('SqliteDB').Value := StreamToSend;
finally
// Don't free StreamToSend ?
end;
end;
Client code
procedure TApp2Form.TetheringAppProfile1Resources0ResourceReceived(const Sender:
TObject; const AResource: TRemoteResource);
var
ReceivedStream : TStream;
FileStream : TFileStream;
begin
FileName := ExtractFilePath(Application.ExeName) + 'Temp.Sqlite';
AResource.Value.AsStream.Position := 0;
FileStream := TFileStream.Create(FileName, fmCreate);
ReceivedStream := AResource.Value.AsStream;
try
ReceivedStream.Position := 0;
FileStream.CopyFrom(ReceivedStream, ReceivedStream.Size);
finally
FileStream.Free;
// ReceivedStream.Free; No! The tethering framework frees the stream
end;
OpenTable;
end;
procedure TApp2Form.OpenTable;
begin
if FDConnection1.Connected then
FDConnection1.Connected := False;
FDConnection1.Params.Clear;
FDConnection1.Params.Add('Database=' + FileName);
FDConnection1.DriverName := 'Sqlite';
try
FDConnection1.Connected := True;
FDQuery1.Open('select * from mytable');
except
ShowMessage(Exception(ExceptObject).Message + ' ' + FileName);
end;
end;
I tested the above in Delphi 10.2.3 on Win10 64-bit and it works fine for me.
If you wanted to copy only a few tables to the client, what I would do is
In the server, open one of the tables in an FDQuery, then assign its data to an
FDMemtable by FDMemTable1.Data := FDQuery1.Data
Call SaveToStream on FDMemTable1 and send the stream as a stream resource to the client
On the client, call FDMemTable.LoadFromStream to load the received stream. I think,
because I haven't tried it that the client would need to contain a TFDPhysSQLiteDriverLink
to support loading from the stream.