ONLINE HELP
 WINDEVWEBDEV AND WINDEV MOBILE

This content has been translated automatically.  Click here  to view the French version.
Help / WLanguage / Managing databases / HFSQL / HFSQL Client/Server functions
  • WLanguage procedure executed in the main thread
  • WLanguage procedure executed in a secondary thread
  • Special cases
WINDEV
WindowsLinuxJavaReports and QueriesUser code (UMC)
WEBDEV
WindowsLinuxPHPWEBDEV - Browser code
WINDEV Mobile
AndroidAndroid Widget iPhone/iPadIOS WidgetApple WatchMac Catalyst
Others
Stored procedures
HWatch (Function)
In french: HSurveille
HFSQL Client/ServerAvailable only with this kind of connection
Warning
From version 2024, HTrack is kept for backward compatibility. This function has been replaced with HWatch.
Trigger monitoring of write actions (add, modify or delete) performed on a data file present on an HFSQL server. In case of modification, a specific procedure can be triggered.
This watch mechanism can be stopped with HWatchStop.
Example
// Lance la surveillance du fichier de données Commande
// La procédure TraiteCommande est appelée pour tout ajout d'enregistrement dans le fichier de données
HWatch(Commande, TraiteCommande, hRecNumAll, hwAdd)
Syntax
<Result> = HWatch(<Data file> , <WLanguage procedure> [, <Record number> [, <Action to watch> [, <Execution mode>]]])
<Result>: Boolean
  • True if the data file watch mechanism is enabled,
  • False otherwise. To get more details on the error, use ErrorInfo.
<Data file>: Optional character string
Name of HFSQL data file to use. The data file is associated with a connection and with a server.
If this parameter is an empty string (""), HWatch manipulates the last data file used by the last HFSQL function (function starting with "H").
<WLanguage procedure>: Procedure name
Name of the WLanguage procedure ("callback") called when a change is made in the specified data file.
For more details on this procedure, see Parameters of the procedure used by HWatch.
<Record number>: Optional integer
  • Number of the record to watch.
  • hRecNumAll constant to watch all the records in the data file.
<Action to watch>: Optional constant (or combination of constants)
Actions to watch for which the procedure will be started:
hwAddMonitors the operations for adding records.
New in version 2025
In previous versions, this constant corresponds to hsAdd.
hwCrossMonitors the operations for crossing records.
New in version 2025
In previous versions, this constant corresponds to hsCross.
hwDeleteMonitors the operations for deleting records.
New in version 2025
In previous versions, this constant corresponds to hsDeletion.
hwModifyMonitors the operations for modifying records.
New in version 2025
In previous versions, this constant corresponds to hsModification.
<Execution mode>: Optional constant
WLanguage procedure execution mode:
hSecondaryThreadExecute the WLanguage procedure in a secondary thread.

By default, the WLanguage procedure is executed in the main thread.
Remarks

WLanguage procedure executed in the main thread

By default, this WLanguage procedure is called in the main thread of the application, with the HFSQL context that corresponds to the procedure:
  • If the procedure is a local procedure of a window that uses an independent context, the context of the window will be used.
  • If the procedure belongs to a component that uses an independent context, the context of the component will be used.
Caution:
The procedure associated with HWatch can be called at any time in the application.
If the procedure reads records or moves between records in the data files, this will have an impact on the application (like the timers).
It may therefore be necessary to use: Multitask must not be used in the procedure code.

For more details on this procedure, see Parameters of the procedure used by HWatch.

WLanguage procedure executed in a secondary thread

If the WLanguage procedure is called in a secondary thread:
  • the HFSQL context is copied the first time HWatch is called. Only the directories containing the data files in HFSQL Classic mode and/or the connections in HFSQL Client/Server mode are stored.
    Note: If HChangeDir is called between two calls to the HWatch function, HChangeDir is ignored. Example:
    HWatch(UnFichier, hSecondaryThread)
    // La fonction HChangeRep n'est pas prise en compte
    HChangeDir(UnAutreFichier)
    HWatch(UnAutreFichier, hSecondaryThread)
  • UI elements (windows, controls, etc.) cannot be manipulated in the secondary thread. When a secondary thread must interact with the user or update the UI, it must use a process started from the main thread. This process can correspond to:
    • a global procedure of the project or a local procedure (of a window, etc.) called by ExecuteMainThread,
    • the "Request for refreshing the display" event of a window run by RequestRefreshUI.
For more details on this procedure, see Parameters of the procedure used by HWatch.

Special cases

Watching is defined for a data file and a connection:
  • If the physical name or the connection associated with the logical file name changes, the file watched by the server remains the one specified during the call to HWatch.
  • If the connection is closed, the watch mechanism is automatically stopped.
  • Watching continues if the connection is lost then restored by automatic reconnection.
To stop watching the data file, use HWatchStop.
Windows service:
HWatch and HWatchStop can be used in a Windows service.
When HWatch is used in a Windows service, it can only be tested on the deployed service, and not when testing the service via the "Go" option.
Business / UI classification: Business Logic
Component: wd300hf.dll
Minimum version required
  • Version 22
This page is also available for…
Comments
Click [Add] to post a comment

Last update: 06/12/2025

Send a report | Local help