HAlias (Function)

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Physical data file associated with an alias
Canceling the aliases of one or more data files
Alias and queries
Handling the alias file and its items
Changing the directory or modifying the connection
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HAlias (Function)

In french: HAlias

Not available with this kind of connection

Creates a logical alias of a data file (or query) or cancels all existing aliases. The alias can also be canceled by HCancelAlias.

Reminder: An alias allows you to work on different physical data files that have the same logical description. For a data file for example, the file description is performed in the analysis and HAlias is used to create the file alias.

Remark: This help page explains how to create an alias with HAlias. Starting with version 27, you can use Alias variables. This type of variable makes it easier to create and handle aliases.

Example

See additional examples

// Data Source variable to handle the alias after its creation
OrderCheck is Data Source <description=Order>
// New feature of version 19 : 
// <description=Order> is used to get the code completion 
// for the items in the Order data file

// Create an alias for the "Order" data file
IF HAlias(Order, OrderCheck) = True THEN
	// "OrderCheck" can now be used in processes.
	// It behaves like the "Order" file described in the analysis.
	// By default, the name of the associated physical file corresponds to 
	// the name of the data source, therfore "OrderCheck" in this case
	// To handle the same physical file as the initial one, the name must be modified:
    HChangeName(OrderCheck, Order.PhysicalName)
    	// To use a file on another database or in another directory,
	// you must use HChangeConnection or HChangeDir
ELSE
    Error("Failure creating the alias", HErrorInfo())
    RETURN
END

Syntax

<Result> = HAlias(<Data file> [, <Alias>])

<Result>: Boolean

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

<Data file>: Character string

Logical name of data file (defined in the analysis) or name of query (created with the query editor).
If this parameter corresponds to "*", all the aliases defined in the current application are canceled. The corresponding data files are automatically closed.

<Alias>: Optional character string or data source

Name of alias, used to define the alias structure.
If this parameter is not specified, all the aliases created for <Data file> are canceled. The corresponding data files are closed.
To optimize your applications, it is recommended to use a variable of type Data source (see example).
The <Alias> file uses the connection parameters of <Data file> (parameters defined in the analysis).

Remarks

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 HChangeConnection, HChangeName and HChangeDir.

Canceling the aliases of one or more data files

The cancellation of an alias (HCancelAlias) closes the associated data file.

To cancel the aliases of a data file, all you have to do is use HAlias without specifying the alias name.

To cancel all the aliases defined on all the data files of current project, all you have to do is use the following syntax:

HAlias("*")

Alias and queries

If the query was created through programming (HExecuteSQLQuery), all you have to do is create the alias query with this same function while specifying the alias name.

If the query was created by the report editor, to create an alias, you must:

run the initial query.
use HAlias and specify the query name as well as the alias name.
use HExecuteQuery with the alias query. The alias is initialized.

For example:

QueryAlias is Data Source
HAlias(QRY_Query1, QueryAlias)
HExecuteQuery(QueryAlias)

Remark: When creating the alias, the initial query must have been run.
Example:

QueryAlias is Data Source 
IF HExecuteQuery(QRY_Query1) = False THEN
	Error(HError(hErrCurrent)) 
ELSE
	HReadFirst(QRY_Query1)
	Trace(QRY_Query1.City)
	HAlias(QRY_Query1, QueryAlias)
	IF HExecuteQuery(QueryAlias) = False THEN
		Error(HError(hErrCurrent)) 
	ELSE
		FOR EACH AliasQuery
			Trace(QueryAlias.City)
		END
	END
END

Handling the alias file and its items

To avoid the "Unknown identifier" error when using an alias file and its items, it is recommended to use a Data source variable to declare the name of the alias before using HAlias.
For example:
```
Order2018 is Data Source
HAlias(Order, Order2018)
```
Caution: the Extern keyword can be used but it slows down the execution significantly.
In HReadSeek, HReadFirst, HReadNext, ... the name of the alias item cannot be used directly: the name of the item must be enclosed in quotes.
For example:
```
HReadSeekFirst(srcAlias, "KeyItem", "Sought Value")
```
The name of the data source must not be used in quotation marks, if Automatic naming of data sources is enabled in the project description window.
In the window or page editor, controls cannot be directly bound to the items of the alias files. You must:
- assign a value to each control in the code.
- use the ControlAlias function or the DataBinding property before calling:
  - the FileToScreen function.
  - the FileToPage function.
Example:
```
ControlAlias(Control, srcAlias)
OR
 ControlAlias(GR_ControlGroup, srcAlias)
OR
 ControlAlias(WIN_Window, srcAlias)
OR
EDT_CustomerName.DataBinding = "SrcAlias.CustomerName"
```
The alias files can be handled by HListItem and HListKey. The alias files can be re-indexed.
By default, the password of an alias file is identical to the password of the initial data file. This password can be changed using HPass. The name of the data file used in this function corresponds to the name of the alias.
The automatic modification of the data files can be applied to the alias files.
The locks performed on the data files or on the records are effective between the aliases of the same instance of an application.

Changing the directory or modifying the connection

If HChangeDir or HConnect have been used with the initial data file, these changes are ignored for the <Alias> data file.

Once an alias was created, we recommend that you use HChangeConnection to define the connection parameters on the alias file.

Previous versions

This function replaces HAlias_55, which is kept for compatibility with WINDEV 5.5.

Component: wd300hf.dll