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  • WLanguage procedure
  • Special cases
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Stored procedures
HTrack (Function)
In french: HSurveille
HFSQL Client/ServerAvailable only with this kind of connection
Starts tracking write actions (addition, modification or deletion) performed on a file found in an HFSQL server. In case of modification, a specific procedure can be triggered.
This track can be stopped by HTrackStop.
Example
// Starts tracking the Order data file
// The ProcessOrder procedure is called whenever a record is added to the data file
HTrack(Order, ProcessOrder, hRecNumAll, hsAdd)
Syntax
<Result> = HTrack(<Data file> , <WLanguage procedure> [, <Record number> [, <Action to track>]])
<Result>: Boolean
  • True if the tracking is enabled,
  • False otherwise. To get the details of the error, use ErrorInfo.
<Data file>: Optional character string (with or without quotes)
Name of HFSQL data file to use. The data file is associated with a connection and with a server.
If this parameter corresponds to an empty string (""), HTrack will use the last data file used by the last HFSQL management function (function starting with "H").
<WLanguage procedure>: Procedure name
Name of WLanguage procedure ("callback" procedure) that will be called when a change is detected in the specified data file.
For more details on this procedure, see Parameters of the procedure used by HTrack.
<Record number>: Optional integer
  • Number of the record to track.
  • hRecNumAll constant to track all the records found in the data file (which means the entire data file).
<Action to track>: Optional constant (or combination of constants)
Actions to track for which the procedure will be started:
hsAddMonitors the operations for adding records.
hsModificationMonitors the operations for modifying records.
hsCrossMonitors the operations for crossing records.
hsDeletionMonitors the operations for deleting records.
Remarks

WLanguage procedure

The WLanguage procedure is called in the main thread of the application, with the HFSQL context corresponding to the procedure:
  • If the procedure is a local procedure of a window that is using an independent context, the context used will be the one of the window.
  • If the procedure belongs to a component that is using an independent context, the context used will be the one of the component.
Caution:
The procedure associated with HTrack can be called at any time in the application.
If the procedure performs HFSQL browses or moves in the data files, this will impact the application (like the timers).
Therefore, you may have to call HSavePosition and HRestorePosition to save the contexts of files used.
Multitask must not be used in the procedure code.

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

Special cases

The track 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 tracked by the server remains the one specified during the call to HTrack.
  • If the connection is closed, the track is automatically stopped.
  • The tracking continues if the connection is lost then restored by automatic reconnection.
To stop tracking the data file, use HTrackStop.
Versions 24 and later
HTrack and HTrackStop can be used in a Windows service.
New in version 24
HTrack and HTrackStop can be used in a Windows service.
HTrack and HTrackStop can be used in a Windows service.
Component : wd250hf.dll
Minimum version required
  • Version 22
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