Overloading a WLanguage function or using a WLanguage function in an SQL query

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Overview
Overload a WLanguage function
Overview
How to overload a WLanguage function?
Differentiating between the WLanguage function and the custom function
Using WLanguage functions in the SQL queries for HFSQL
Overview
How to proceed?
Remarks

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Overloading a WLanguage function or using a WLanguage function in an SQL query

Available only with these kinds of connection

Overview

WLanguage proposes the "WL." keyword to:

Overload a WLanguage function.
Use a WLanguage function in an SQL query run by the HFSQL engine.
Versions 22 and later
Remark: The "WL." keyword also allows you to use a WLanguage constant in an SQL query containing a WLanguage function.
New in version 22
Remark: The "WL." keyword also allows you to use a WLanguage constant in an SQL query containing a WLanguage function.
Remark: The "WL." keyword also allows you to use a WLanguage constant in an SQL query containing a WLanguage function.

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

Overload a WLanguage function

Overview

Overloading a WLanguage function allows you to use a custom function with the same name as the WLanguage function.

For example, instead of using the standard WLanguage function Info, you can use a custom procedure named Info. The custom procedure will be run whenever Info is called.

How to overload a WLanguage function?

To overload a WLanguage function:

Create a new procedure in your project (local or global procedure). This procedure must have the following characteristics:
- The same name as the WLanguage function to overload.
- The same number of parameters as the WLanguage function to overload. These parameters must have the same type as the parameters of the WLanguage function.
The custom procedure will be used instead of the WLanguage function whenever the name of the function/procedure is used in the project (or in the window if the created procedure is a local procedure).

Remarks:

Overloading WLanguage functions is ignored during the dynamic compilation. For example, if Trace has been overloaded, the WLanguage function (not the overloaded function) will be called in a code that is dynamically compiled.
Versions 19 and later
You have the ability to overload functions that handle windows, pages or reports. All you have to do is use the following notation to define the parameter corresponding to the requested element in the procedure that overloads the function:
- For the pages, the parameter must be defined by the following notation "PageName is string <page name>". For example, to overload PageDisplay, the procedure code will be:
  
  PROCEDURE PageDisplay(PageName is string <page name>, *)
- For the reports, the parameter must be defined by the following notation "ReportName is string <report name>". For example, to overload iPrintReport, the procedure code will be:
  
  PROCEDURE iPrintReport(ReportName is string <report name>, *)
See Parameters of a procedure for more details.
New in version 19
You have the ability to overload functions that handle windows, pages or reports. All you have to do is use the following notation to define the parameter corresponding to the requested element in the procedure that overloads the function:
- For the pages, the parameter must be defined by the following notation "PageName is string <page name>". For example, to overload PageDisplay, the procedure code will be:
  
  PROCEDURE PageDisplay(PageName is string <page name>, *)
- For the reports, the parameter must be defined by the following notation "ReportName is string <report name>". For example, to overload iPrintReport, the procedure code will be:
  
  PROCEDURE iPrintReport(ReportName is string <report name>, *)
See Parameters of a procedure for more details.
You have the ability to overload functions that handle windows, pages or reports. All you have to do is use the following notation to define the parameter corresponding to the requested element in the procedure that overloads the function:
- For the pages, the parameter must be defined by the following notation "PageName is string <page name>". For example, to overload PageDisplay, the procedure code will be:
  
  PROCEDURE PageDisplay(PageName is string <page name>, *)
- For the reports, the parameter must be defined by the following notation "ReportName is string <report name>". For example, to overload iPrintReport, the procedure code will be:
  
  PROCEDURE iPrintReport(ReportName is string <report name>, *)
See Parameters of a procedure for more details.

Differentiating between the WLanguage function and the custom function

If a WLanguage function was overloaded and if you want to use the initial function, the name of the function must be prefixed by WL. The following syntax must be used:

WL.<Function name>

For example, to override the WLanguage function Trace, you can use the following code:

PROCEDURE Trace(Information1)
Message("Start a trace")
WL.Trace(Information1)

Using WLanguage functions in the SQL queries for HFSQL

Overview

A WLanguage function can be used in an SQL query. This SQL query can be run on HFSQL files. You can for example use the WLanguage functions to create advanced selection conditions.

The WLanguage functions can be used in the SQL code of a query or in the query editor (for example, when creating a calculation item that is using a mathematical formula).

How to proceed?

To use WLanguage functions in the queries for HFSQL:

Create a query in the query editor.
To use the WLanguage functions in the query, use the following notation: WL.<Function name>
The WLanguage functions can be used for example:
- In the SQL code of the query. Example:
  
  -- Selecting the tasks exceeding 5 days
  SELECT Task.Caption FROM Task WHERE
  WL.DateDifference(Task.StartDate, Task.EndDate) > 5
- In a mathematical formula handled by a calculated item.
The query can be:
- run in the query editor directly,
- run by HExecuteSQLQuery (for an SQL query) or by HExecuteQuery.

Remarks

Only the WLanguage functions can be used in the queries. The properties cannot be used.
Several WLanguage functions can be nested in a query.
If the WLanguage functions is used in SELECT, the returned value is a text memo.
This syntax can only be used with HFSQL Classic, Mobile and Client/Server.
The limits of the WLanguage function are identical if the function is used in a query.
The following functions are available in the queries:
- The functions for managing character strings (Right, Left, StringToDate, ...).
- The functions for managing dates (DateSys, DateToInteger, ...).
- The functions for managing integers (IsOdd, IsEven, Exp, ...).
- The functions for managing text files.
- The functions for managing INI files.
- The functions for managing the registry.
To use Open, OpenChild and OpenPopup in the queries, the name of windows must be passed in character string format (between quotes).
Versions 22 and later
To use a WLanguage constant in the queries containing WLanguage functions, use the following notation: WL.<Constant name>
For example, SQL code of query:

SELECT
WL.ExtractString('A|B|C',1,'|'),
WL.ExtractString('A|B|C',1,'|', WL.FromEnd)
FROM
DUAL

New in version 22
To use a WLanguage constant in the queries containing WLanguage functions, use the following notation: WL.<Constant name>
For example, SQL code of query:

SELECT
WL.ExtractString('A|B|C',1,'|'),
WL.ExtractString('A|B|C',1,'|', WL.FromEnd)
FROM
DUAL

To use a WLanguage constant in the queries containing WLanguage functions, use the following notation: WL.<Constant name>
For example, SQL code of query:

SELECT
WL.ExtractString('A|B|C',1,'|'),
WL.ExtractString('A|B|C',1,'|', WL.FromEnd)
FROM
DUAL

Related Examples:

Unit examples (WINDEV): Overloading WLanguage functions

[ + ] Overloading WLanguage functions.
This example overloads the Trace function and it is used to:
- Display a "normal" trace
- Display a trace and save the data in a file
- Perform a file trace (the information is saved in a file)