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Steve Bailey · Guest

I have a TADOConnection on a DataModule connecting to a database using the
Microsoft OLE DB Provider for ODBC Drivers (MSDASQL.1).

When I my application executes ADOConnection1.Close and I watch it with ODBC
trace it is apparent that there is no SQLDisconnect command sent to the
database.

Looking in DB.pas I see:

procedure TCustomConnection.Close;
begin
SetConnected(False);
end;

procedure TCustomConnection.SetConnected(Value: Boolean);
begin
if (csReading in ComponentState) and Value then
FStreamedConnected := True else
begin
if Value = GetConnected then Exit;
if Value then
begin
if Assigned(BeforeConnect) then BeforeConnect(Self);
DoConnect;
SendConnectEvent(True);
if Assigned(AfterConnect) then AfterConnect(Self);
end else
begin
if Assigned(BeforeDisconnect) then BeforeDisconnect(Self);
SendConnectEvent(False);
DoDisconnect;
if Assigned(AfterDisconnect) then AfterDisconnect(Self);
end;
end;
end;

procedure TCustomConnection.DoDisconnect;
begin
end;

procedure TCustomConnection.SendConnectEvent(Connecting: Boolean);
var
I: Integer;
ConnectEvent: TConnectChangeEvent;
begin
for I := 0 to FClients.Count - 1 do
begin
if FConnectEvents[I] <> nil then
begin
TMethod(ConnectEvent).Code := FConnectEvents[I];
TMethod(ConnectEvent).Data := FClients[I];
ConnectEvent(Self, Connecting);
end;
if TObject(FClients[I]) is TDataset then
TDataSet(FClients[I]).DataEvent(deConnectChange, Integer(Connecting));
end;
end;

TCustomConnection.DoDisconnect is empty. Is that right? Does that explain
why my application appears to do nothing when ADOConnection1.Close is
executed?

Brian Bushay TeamB · Guest

Steve Bailey · Guest

OK. BTW, my original post asked about TCustomConnection.DoDisconnect being
empty. I should, of course, have looked further than that. DoDisconnect is
a virtual method, overridden by TADOConnection.DoDisconnect, which calls
TADOConnection.ConnectionObject.Close. After that it calls code which, I'm
afraid, is beyond me.

My TADOConnection's Provider is "Microsoft OLE DB Provider for ODBC Drivers
(MSDASQL.1)". One of the first ODBC calls MSDASQL must make is to
initialize the ODBC environment: "SQLAllocHandle". This returns a handle.

Is there any way of getting at this handle through TADOConnection? (If
there is then I can call SQLDisconnect myself.)

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Vitali Kalinin · Guest

Most probably you are observing ODBC connection pooling in action. - "When
the application releases the connection, the pool returns S_OK to the user,
simulating a successful disconnection from the database. However, the actual
connection is not released by ODBC but instead waits in the pool. When the
next request for a connection to the database that has the same data source
and user information comes in, it is satisfied from the connection in the
pool rather than by making a full connection to the database."

Steve Bailey · Guest

Thanks for that, Vitali.

Is there any way I can switch off Connection Pooling (at least temporarily)
from within my application?

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Steve Bailey · Guest

I have just checked and can confirm that Connection Pooling is actually
disabled on my development machine so, unfortunately, it looks like it is
not the cause of my problem.

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Vitali Kalinin · Guest

Have you tried to disable OLE DB pooling also (append yours connection
string with ";OLE DB Services = -2")?

Brian Bushay TeamB · Guest

Steve Zimmelman · Guest

Try using the SQLOLEDB provider instead of the ODBC version.

-Steve-

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Steve Bailey · Guest

Thank you Vitali!

That works nicely. I was not aware of OLE DB pooling.

You are a star!

Steve.

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Steve Bailey · Guest

I never said it was SQL Server. It's actually Mimer SQL Engine 9.2.

ODBC is the best way to connect to it for a Delphi Win32 application.

It makes no difference to TADOConnection and MSDASQL - they just work
together to call the appropriate ODBC SQL functions and they do absolutely
nothing when ADOConnection.Close is called.

If possible, I need some way of forcing them to call SQLDisconnect or some
way of finding out the ODBC Environment handle so I can call SQLDisconnect
manually.

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