HCancelDeclaration (Function)

Delete a declaration that was performed beforehand by HDeclare, HDeclareExternal, HDescribeFile. After this operation, the data file is no longer recognized by the HFSQL engine.
Free the resources of a query (after the call to HExecuteQuery or HExecuteSQLQuery).

Versions 15 and later

This function is now available for Android applications.

New in version 15

This function is now available for Android applications.

Versions 17 and later

This function is now available for iPhone/iPad applications.

New in version 17

This function is now available for iPhone/iPad applications.

Versions 18 and later

This function is now available in Android Widget mode.

This function is now available in Windows Store apps mode.

New in version 18

This function is now available in Android Widget mode.

This function is now available in Windows Store apps mode.

This function is now available in Android Widget mode.

This function is now available in Windows Store apps mode.

Versions 21 and later

This function is now available in Universal Windows 10 App mode.

New in version 21

This function is now available in Universal Windows 10 App mode.

Note: From version 19, HFSQL is the new name of HyperFileSQL.

Example

See additional examples

// The Customer file was declared beforehand in the analysis
// by HDeclareExternal
HClose(Customer)
HCancelDeclaration(Customer)

Syntax

<Result> = HCancelDeclaration([<File name>])

<Result>: Boolean

True if the operation was performed,
False if a problem occurred. HError is used to identify the error.

<File name>: Optional character string (with or without quotes)

Corresponds to:
the name of data file (defined in the analysis). If this name is not specified, HCancelDeclaration refers to the last data file used.
the name of query or data source associated with a query (when freeing resources once HExecuteQuery or HExecuteSQLQuery has been used).

Remarks

Conditions for using HCancelDeclaration

This function must be used ONLY when the relevant data file (or query) is not used anymore!

In the following example, HCancelDeclaration is used too soon: the table will be completely wrong. Indeed, BuildBrowsingTable (used to fill the table) is run in background task in a parallel process. Therefore, HCancelDeclaration will operate before the table is entirely filled, making this table unusable.

HExecuteSQLQuery("test", "select * from customer")
BuildBrowsingTable(TABLE_Table1, "test")
HCancelDeclaration("test")

Note: The problem can also occur with a "data source" variable. A "data source" variable declared locally in a process (button click, procedure, method, etc.) ONLY exists during the execution of this code. For this reason, a "warning" is displayed when you are using this type of data source: "the data source will be destroyed at the end of this code".

HCancelDeclaration and closing the data file

To use HCancelDeclaration on a data file, this data file must be closed.

If a query, a sub-query or a view is using the data file, HCancelDeclaration cannot be run even after a call to HClose. The queries or views that are using the data file must be freed beforehand.

Component : wd240hf.dll