HDescribeTrigger (Function)

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Trigger on the table functions
Variables used to manage the triggers
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HDescribeTrigger (Function)

In french: HDécritTrigger

Not available with these kinds of connection

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 and DELETE queries also trigger execution of the trigger (note: the trigger is not triggered on tables accessed via a Native Connector).

For more details, see Managing triggers.

This function is only available on the client side. Use HDescribeServerTrigger to define a server trigger for an HFSQL Client/Server database.

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("Trigger error: " + 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:
HModify
HAdd
HDelete
HWrite
HCross

<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.
hTriggerAfter The procedure is run after the HFSQL function.
hTriggerBefore The procedure is run before the HFSQL function.

Remarks

Trigger on the table functions

Table manipulation functions (TableAdd, TableAddLine, TableDelete, TableModify, etc.) implicitly use the following HFSQL functions: HAdd, HDelete and HModify.

When using one of these functions for handling 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 (or stored procedure) receives no parameters. However, some HFSQL state variables are positioned before each call:


H.FileName	Character string: Logical name of the data file for which the trigger is activated. Warning Depending on the logical name used by the application, the value of the variable H.FileName variable may be different (using aliases, for example). It is recommended to use: MyFile.DescribedName for the logical name of the file being handled (without taking aliases into account). MyFile.PhysicalName to find out the physical name of the file being handled.
H.Action	Character initialized to "A" for a Before trigger and to "P" for an After trigger.
H.TriggerFunction	String: Name of the HFSQL function that triggered the trigger. Warning The variable H.FunctionTrigger variable is deprecated in favour of the H.FunctionTriggerNumber. The information given by the variable is independent of the language used to run the application.
New in version 2025 H.TriggerFunctionNumber	Constant used to identify the function that triggered the trigger: htrgHAjoute The function that triggered the trigger is HAdd. htrgHEcrit The function that triggered the trigger is HWrite. htrgHModifies: The function that triggered the trigger is HModify. htrgHRaye: The function that triggered the trigger is HCross. htrgHSupprime The function that triggered the trigger is HDelete.
H.ToDo	During the execution of a before trigger: cancelling the execution of the current 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). cancelling the execution of the ongoing HFSQL function by assigning "E" to the HFSQL state variable: H.AFaire = "E". In this case, the action is not performed and the function (HAdd, HModify, etc.) returns False. The error message reads: "The action on file XXX has been interrupted by the trigger".

Note In the case where a "BEFORE" and an "AFTER" trigger are associated with an HFSQL function, if the "BEFORE" trigger cancels the execution of the HFSQL function (by setting H.AFaire to "A"), the "AFTER" trigger is not triggered.

Previous versions

This function replaces HDescribeTrigger_55, which is kept for compatibility with WINDEV 5.5.

Component: wd300hf.dll