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  • Trigger on the table management functions
  • Variables used to manage the triggers
  • Previous versions
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Stored procedures
Adds or modifies a trigger on an HFSQL data file. A trigger is a WLanguage procedure automatically called by the HFSQL engine whenever an HFSQL function is run. UPDATE, INSERT or DELETE queries also execute the trigger (Caution: the trigger is executed on tables accessed via a Native Connector).
For more details, see Managing triggers.
HFSQLHFSQL Client/Server This function is only available on the client side. Use HDescribeServerTrigger to define a server trigger for an HFSQL Client/Server database.
Versions 17 and later
iPhone/iPad This function is now available for iPhone/iPad applications.
New in version 17
iPhone/iPad This function is now available for iPhone/iPad applications.
iPhone/iPad This function is now available for iPhone/iPad applications.
Versions 18 and later
Universal Windows 10 App This function is now available in Windows Store apps mode.
New in version 18
Universal Windows 10 App This function is now available in Windows Store apps mode.
Universal Windows 10 App This function is now available in Windows Store apps mode.
Versions 21 and later
Universal Windows 10 App This function is now available in Universal Windows 10 App mode.
New in version 21
Universal Windows 10 App This function is now available in Universal Windows 10 App mode.
Universal Windows 10 App This function is now available in Universal Windows 10 App mode.
Remark: From version 19, HFSQL is the new name of HyperFileSQL.
Example
// In the initialization code of the project
LOCAL
TriggerResult is boolean
 
// Create a trigger for all the analysis files
TriggerResult = HDescribeTrigger("*", "HADD,HMODIFY," + ...
 "HDELETE, HCROSS,HWRITE", "CheckUserRights", hTriggerBefore)
// "CheckUserRights" is a global procedure of the project
IF TriggerResult = False THEN
 Error("Error on a trigger: " + HErrorInfo)
 RETURN
END
Syntax
<Result> = HDescribeTrigger(<List of HFSQL data files> , <List of HFSQL functions> , <WLanguage procedure> , <Type of trigger>)
<Result>: Boolean
  • True if the operation was performed,
  • False if a problem occurs. HErrorInfo is used to identify the error.
<List of HFSQL data files>: Character string
Logical name of one or more HFSQL data files.
To specify several names of data files, the names of the data files must be separated by a comma (",").
To use all the data files found in the analysis, this parameter must be equal to "*".
<List of HFSQL functions>: Character string
Name of one or more HFSQL or TableXXX functions on which the trigger must be implemented. To specify several names of functions, the names of functions must be separated by a comma (","). You have the ability to define triggers on the following functions:
<WLanguage procedure>: Procedure name
Name of the WLanguage procedure that will be run when a trigger is activated on the specified HFSQL functions.
<Type of trigger>: Integer constant
Indicates the type of trigger.
hTriggerAfterThe procedure is run after the HFSQL function.
hTriggerBeforeThe procedure is run before the HFSQL function.
Remarks

Trigger on the table management functions

The table management functions (TableAdd, TableAddLine, TableDelete, TableModify, ... ) implicitly use the following HFSQL functions: HAdd, HDelete and HModify.
When using one of these functions for handling the tables, if a trigger is defined for the corresponding HFSQL function, the trigger is automatically activated.

Variables used to manage the triggers

A trigger procedure accepts no parameter. However, some HFSQL state variables are positioned before each call:
H.ActionCharacter initialized to "A" for a Before trigger and to "P" for an After trigger.
H.FileNameCharacter string: Logical name of the data file whose trigger is activated
H.ToDoDuring the execution of a before trigger:
  • cancel the execution of the HFSQL function by assigning "A" to the HFSQL state variable: H.ToDo = "A". In this case, the action is not performed and the function (HAdd, HModify, etc.) returns True (no error).
  • cancel the execution of the current HFSQL function by assigning "E" to the HFSQL state variable: H.ToDo = "E". In this case, the action is not performed and the function (HAdd, HModify, etc.) returns False. The error message is as follows: "The action on XXX file was interrupted by the trigger".
H.TriggerFunctionCharacter string: Name of the HFSQL function that activated the trigger

Remark: When a "BEFORE" trigger and an "AFTER" trigger are associated with an HFSQL function, if "BEFORE" cancels the execution of the HFSQL function (by setting H.ToDo to "A"), "AFTER" is not run.
WINDEV

Previous versions

This function replaces HDescribeTrigger_55, which is kept for compatibility with WINDEV 5.5.
Component: wd270hf.dll
Minimum version required
  • Version 9
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Comments
Not only on HFCS databases
According to the online help: HdescribeTrigger "Adds or modifies a trigger on a HFSQL data file"

I have used HdesdcribeTrigger on Postgresql databases also.
Diego Sanchez
04 Feb. 2015