Link description (Type of variable)

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Properties specific to the link description
How to describe the data files by programming?
Handling the links of a data file described by programming

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Link description (Type of variable)

In french: Description de liaison (Type de variable)

Available only with these kinds of connection

A Link description variable is used to describe a link between two data files by programming. The description of each link is validated by HDescribeLink.

After this validation:

This link can be handled like any other link described in the analysis.
The "Link description" variable is reinitialized and it can be used to describe another link by programming.

Versions 17 and later

This type of variable is now available for iPhone and iPad applications.

New in version 17

This type of variable is now available for iPhone and iPad applications.

Versions 18 and later

This type of variable is now available in Windows Store apps mode.

New in version 18

This type of variable is now available in Windows Store apps mode.

Versions 21 and later

This type of variable is now available in Universal Windows 10 App mode.

New in version 21

This type of variable is now available in Universal Windows 10 App mode.

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

Example

MyLink is Link Description
MyLink1, MyLink2 are Link Descriptions

// Describe and validate City and Customer data files
...

// Describe the "LIVES" link
MyLink is Link Description
MyLink.Name = "LIVES"
MyLink.SourceFile = "CITY"
MyLink.LinkedFile = "CUSTOMER"
MyLink.SourceKey = "CITYNAME"
MyLink.LinkedKey = "CUSTCITY"
// Default link (0-1, 0-1)

// Validate the description of the "LIVES" link
HDescribeLink(MyLink)

Syntax

Declaring one or more link descriptions Hide the details

<Variable name> is Link Description
<Variable name 1>, <Variable name 2> are Link Descriptions

<Variable name>:

Name of the "Link description" variable to declare.
Remark: The a and an keywords are optional: they provide better readability.

Describing a "Link description" variable Hide the details

To describe a "Link description" variable:
Use the WLanguage properties specific to the link descriptions. For more details, see remarks.

To validate the description of a "Link Description" variable:
Use HDescribeLink.

Remarks

Properties specific to the link description

The following properties are specific to the link descriptions:

Remark: The properties written in bold followed by a star must necessarily be initialized when a link is described by programming.

Property name	Effect

MaxLinkedCardinality	Maximum cardinality of the linked item in a link
MinLinkedCardinality	Minimum cardinality of the linked item in a link
MaxSourceCardinality	Maximum cardinality of the source item in a link
MinSourceCardinality	Minimum cardinality of the source item in a link
*LinkedKey ( )**	Item of the linked file used in the link
*SourceKey ( )**	Item of source file used in the link
*LinkedFile ( )**	Name of the linked file used in the link
*SourceFile ( )**	Name of the source file used in the link
*Name ( )**	Name of the link
ModificationRule	Modification rule (integrity management) used in a link
DeletionRule	Deletion rule (integrity management) used in a link

By default, the cardinalities of the link are (0-1) / (0-1).

How to describe the data files by programming?

To describe the data files by programming, you must:

Declare variables of type "File description", "Item description", "FullTextIndex description" and "description de liaison" (if necessary).
For each data file:
- Describe the of the data file characteristics using HFSQL properties .
- Describe the characteristics of the items using HFSQL properties .
- Validate the description of each item (HDescribeItem).
- Describe, if necessary, the characteristics of full-text indexes using HFSQL properties .
- Validate the description of each full-text index (HDescribeFullTextIndex).
- Validate the description of the data file (function HDescribeFile).
Describe (if necessary) the characteristics of links via the HFSQL properties.
If necessary, validate the description of each link (HDescribeLink function).

Handling the links of a data file described by programming

When a link is created in the data model editor, the name of the link is automatically recognized by the compiler.

When creating a link using a variable of type "description of link", the name of this link is defined thanks to the Property nom. This name is not automatically recognized by the compiler. Using this name to identify the link generates a compilation error.

In order for the name of the link created by programming to be recognized by the compiler, this name must be declared via the External keyword. This link can now be handled by its name in the code editor.

For example:

MyLink is Link Description
...
MyLink.Name = "LIVES"
...
HDescribeLink("LIVES")
...
EXTERN LIVES
...
Cardinality = LIVES.MaxLinkedCardinality