HCancelDeclaration (Function)

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Conditions for using HCancelDeclaration
HCancelDeclaration and closing the data file

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HCancelDeclaration (Function)

In french: HAnnuleDéclaration

Not available with this kind of connection

Allows you to:

Delete a declaration previously made with HDeclare, HDeclareExternal, HDescribeFile. After this operation, the data file is no longer recognized by the HFSQL engine.
Free the resources of a query (after calling HExecuteQuery or HExecuteSQLQuery).

Example

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

Syntax

<Result> = HCancelDeclaration([<Data file>])

<Result>: Boolean

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

<Data file>: Optional character string

Corresponds to:
the name of data file (defined in the analysis). If this name is not specified, HCancelDeclaration handles 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, the HCancelDeclaration function is used too early: the contents of the Table field will be completely distorted. The Table control is populated using BuildBrowsingTable in a parallel process in the background. Therefore, HCancelDeclaration will be called before the table is entirely filled, making this table unusable.

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

Remark: The problem can also occur with a variable of type "data source".. A "data source" variable declared locally in a process or event (button click, procedure, method, etc.) ONLY exists while this code is run. For this reason, a "warning" is displayed if you use 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 subquery or a view uses the data file, HCancelDeclaration cannot be executed, even after calling HClose. The queries or views that are using the data file must be freed beforehand.

Component: wd300hf.dll