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unit PQEventMonitor;
{ PostGresql notification monitor
Copyright (C) 2012 Ludo Brands
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version with the following modification:
As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent modules,and
to copy and distribute the resulting executable under terms of your choice,
provided that you also meet, for each linked independent module, the terms
and conditions of the license of that module. An independent module is a
module which is not derived from or based on this library. If you modify
this library, you may extend this exception to your version of the library,
but you are not obligated to do so. If you do not wish to do so, delete this
exception statement from your version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License
for more details.
You should have received a copy of the GNU Library General Public License
along with this library; if not, write to the Free Software Foundation,
Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
}
{$mode objfpc}{$H+}
{$Define LinkDynamically}
interface
uses
Classes, SysUtils,pqconnection,db,dbconst,
{$IfDef LinkDynamically}
postgres3dyn;
{$Else}
postgres3;
{$EndIf}
type
TEventAlert = procedure(Sender: TObject; EventName: string; EventCount: longint;
var CancelAlerts: boolean) of object;
TErrorEvent = procedure(Sender: TObject; ErrorCode: integer) of object;
{ TPQEventMonitor }
TPQEventMonitor=class (TComponent)
private
FConnection: TPQConnection;
FDBHandle: PPGconn;
FErrorMsg: string;
FEvents: TStrings;
FOnError: TErrorEvent;
FOnEventAlert: TEventAlert;
FRegistered: Boolean;
function GetNativeHandle: pointer;
procedure SetConnection(AValue: TPQConnection);
procedure SetEvents(AValue: TStrings);
procedure SetRegistered(AValue: Boolean);
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
procedure Poll;
procedure RegisterEvents; virtual;
procedure UnRegisterEvents; virtual;
property ErrorMsg:string read FErrorMsg;
property NativeHandle: pointer read GetNativeHandle;
published
property Connection: TPQConnection read FConnection write SetConnection;
property Events: TStrings read FEvents write SetEvents;
property Registered: Boolean read FRegistered write SetRegistered;
property OnEventAlert: TEventAlert read FOnEventAlert write FOnEventAlert;
property OnError: TErrorEvent read FOnError write FOnError;
end;
implementation
ResourceString
SErrConnectionFailed = 'Connection to database failed';
SErrExecuteFailed = 'Execution of query failed';
{ TPQEventMonitor }
function TPQEventMonitor.GetNativeHandle: pointer;
begin
result:=FDBHandle;
end;
procedure TPQEventMonitor.SetConnection(AValue: TPQConnection);
begin
if FConnection=AValue then Exit;
If not (csDesigning in ComponentState) and FRegistered then
begin
if assigned(FConnection) then
FConnection.RemoveFreeNotification(self); // remove us from the old connection
UnRegisterEvents;
FConnection:=AValue;
if assigned(FConnection) then
begin
RegisterEvents;
end;
end
else
FConnection:=AValue;
if assigned(FConnection) then
FConnection.FreeNotification(Self); //in case Connection is destroyed before we are
end;
procedure TPQEventMonitor.SetEvents(AValue: TStrings);
begin
FEvents.Assign(AValue);
end;
procedure TPQEventMonitor.SetRegistered(AValue: Boolean);
begin
if not (csDesigning in ComponentState) then
if AValue then
RegisterEvents
else
UnRegisterEvents;
end;
constructor TPQEventMonitor.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FEvents:=TStringList.Create;
{$IfDef LinkDynamically}
InitialisePostgres3; // stick to library in case connection closes before us
{$EndIf}
end;
destructor TPQEventMonitor.Destroy;
begin
if FRegistered then
UnRegisterEvents;
if assigned(FConnection) then
FConnection.RemoveFreeNotification(self);
FEvents.Free;
{$IfDef LinkDynamically}
ReleasePostgres3;
{$EndIf}
inherited Destroy;
end;
procedure TPQEventMonitor.Poll;
var
notify:PpgNotify;
CancelAlerts:boolean;
begin
if FConnection.Connected and FRegistered and (PQconsumeInput(FDBHandle)=1) then
begin
CancelAlerts:=false;
repeat
notify:=PQnotifies(FDBHandle);
if assigned(notify) then
begin
if assigned(OnEventAlert) then
OnEventAlert(Self,notify^.relname,1,CancelAlerts);
PQfreemem(notify);
end;
until not assigned(notify) or CancelAlerts;
if CancelAlerts then
UnRegisterEvents;
end;
end;
procedure TPQEventMonitor.RegisterEvents;
var
i:Integer;
sConn: String;
res: PPGresult;
msg:string;
notify:PpgNotify;
CancelAlerts:boolean;
begin
If not assigned(FConnection) then
DatabaseError(SErrNoDatabaseAvailable,Self);
if not(csDesigning in ComponentState) and not FRegistered and (Events.Count>0) then
begin
sConn := '';
if (FConnection.UserName <> '') then sConn := sConn + ' user=''' + FConnection.UserName + '''';
if (FConnection.Password <> '') then sConn := sConn + ' password=''' + FConnection.Password + '''';
if (FConnection.HostName <> '') then sConn := sConn + ' host=''' + FConnection.HostName + '''';
if (FConnection.DatabaseName <> '') then sConn := sConn + ' dbname=''' + FConnection.DatabaseName + '''';
if (FConnection.Params.Text <> '') then sConn := sConn + ' '+FConnection.Params.Text;
FDBHandle := PQconnectdb(pchar(sConn));
if (PQstatus(FDBHandle) <> CONNECTION_OK) then
begin
msg := PQerrorMessage(FDBHandle);
PQFinish(FDBHandle);
DatabaseError(sErrConnectionFailed + ' (TPQEventMonitor: ' + Msg + ')',self);
end;
for i:=0 to Events.Count-1 do
begin
res := PQexec(FDBHandle,pchar('LISTEN '+ Events[i]));
if (PQresultStatus(res) <> PGRES_COMMAND_OK) then
begin
msg := PQerrorMessage(FDBHandle);
PQclear(res);
PQFinish(FDBHandle);
FDBHandle:=nil;
DatabaseError(SErrExecuteFailed + ' (TPQEventMonitor: ' + Msg + ')',self);
end
else
PQclear(res);
end;
FRegistered :=true;
end;
end;
procedure TPQEventMonitor.UnRegisterEvents;
var
i: Integer;
res: PPGresult;
msg:string;
begin
if not (csDesigning in ComponentState) and FRegistered then
begin
for i:=0 to Events.Count-1 do
begin
res := PQexec(FDBHandle,pchar('unlisten '+ Events[i]));
if (PQresultStatus(res) <> PGRES_COMMAND_OK) then
begin
msg := PQerrorMessage(FDBHandle);
PQclear(res);
PQFinish(FDBHandle);
FDBHandle:=nil;
DatabaseError(SErrExecuteFailed + ' (TPQEventMonitor: ' + Msg + ')',self);
end
else
PQclear(res);
end;
PQFinish(FDBHandle);
FDBHandle:=nil;
FRegistered :=false;
end;
end;
end.
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