Managing aliases on the data files

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Managing aliases on the data files

Overview

Handling the aliases by programming

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Overview
Several physical data files with an identical logical description
Several logical data files linked to a single physical data file
Handling the aliases by programming
The WLanguage functions
Create an alias on what?
Characteristics of an alias
Handling the alias file and its items

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Functions for HFSQL management

Managing aliases on the data files

Available only with these kinds of connection

Overview

The aliases are used to handle:

Several physical data files with the same description in the analysis
Several logical data files described in the analysis that handle the same physical data file.

Versions 17 and later

This feature is now available for iPhone/iPad applications.

New in version 17

This feature is now available for iPhone/iPad applications.

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

Several physical data files with an identical logical description

For example: You have the ability to manage at the same time:

The Customer2000.fic file that contains the backup of the customers for the year 2000
The Customer.fic file that contains the customer references for the current year

These two data files have the same logical description in the analysis: the CUSTOMER file. By default, the description of CUSTOMER file found in the analysis is linked to the Customer.fic file.

To use the Customer2000.Fic data file, you must "copy" the description of the CUSTOMER data file found in the analysis: to do so, create an alias with HAlias. The corresponding code line is as follows:

HAlias(Customer, Customer2000)

The two files will be handled the same way with the HFSQL functions.

Several logical data files linked to a single physical data file

You have the ability to perform several parallel searches on the same physical data file or a search and a filter in parallel on the data file.

Example: The Customer.Fic data file is associated with the logical file named Customer in the analysis. To filter the records found in the Customer.fic data file and to browse at the same time all the records found in this data file, you must:

"Copy" the description of the CUSTOMER data file into the analysis: to do so, create an alias with HAlias.
Associate the description of the alias with the physical data file named Customer.Fic (HChangeName).

Remark: This method is used to manage several HFSQL contexts for the same physical data file.

Handling the aliases by programming

The WLanguage functions

Several functions are used to handle the aliases:


Versions 09 and later HAlias New in version 09 HAlias HAlias	Creates a logical alias of data file (or query) or cancels all existing aliases.
Versions 09 and later HCancelAlias New in version 09 HCancelAlias HCancelAlias	Cancels an alias that was declared beforehand by HAlias.

Other functions can intervene in the definition and use of aliases:


Versions 09 and later HChangeDir New in version 09 HChangeDir HChangeDir	Modifies the access path to a data file (which means the directory where the file will be used).
Versions 09 and later HChangeName New in version 09 HChangeName HChangeName	Modifies the physical name of a data file.

Create an alias on what?

You have the ability to create and handle aliases for the following elements:

Data file described in the analysis
Data file described dynamically
Query created in the query editor
HFSQL Classic view
Alias

Characteristics of an alias

Physical data file associated with an alias:
By default, the name specified for the alias is assigned to the physical data file corresponding to the alias. To associate the alias with a physical data file of different name, you must use HChangeName and HChangeDir.
Password of an alias:
By default, the password of an alias file is identical to the password of the source data file. This password can be modified by HPass. The name of the data file used in this function corresponds to the name of the alias.
Re-indexing:
The alias files can be re-indexed.
Automatic modification of the data files:
This operation can be applied to the alias files.

Handling the alias file and its items

Code editor: To avoid the "Unknown identifier" error when using an alias file and its items, we recommend that you use a data source to declare the name of the alias before using HAlias.
For example:

Orders2000 is Data Source
HAlias(Orders, Orders2000)

Caution: the Extern keyword can be used but it slows down the execution significantly.
Window editor or page editor: the controls and the tables cannot be directly associated with the items found in the alias files. The controls must be assigned one by one by programming.
Remark: to redefine the links of controls by programming, you have the ability to use ControlAlias or ..FileLink.