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From GeneXus 8.0 RC: Auto-numbering Property

This attribute property enables automatic numbering of a transaction's primary key for a given level.

This feature offers higher code legibility and data base integrity; it also gives power to programming. This means that instead of defining a given numbering that depends on the application calling it, the developer makes sure that there will be no "holes" generated in the numbering, which will be configured on the database.

Description
When a table has a simple key, (which means that it is made up of a single attribute), and there is a numerical data-type, it may be automatically numbered by using the feature provided by database handlers with this aim in mind. The way to do this in GeneXus is by configuring the auto-number property from the table's key attribute. For this, it is necessary to be in the design model and configure the key attribute's advanced properties of the auto-number group.
When using the "Enabled" property, the automatic generation of the numbering in the associated table is defined. This only affects database creations/reorganizations.
When using the "Star" property, you may configure what will be the starting number in order to proceed with automatic numbering. The "Step" property enables you to configure the increase for the field (between two records).

Does it apply to compound keys?
No. It only applies when the attribute is, in itself, a table's key. It does not apply for compound keys or secondary attributes. For instance, for second-level auto-numbering the rule serial or a numbering procedure must be used.

Is the property valid in procedures?
Yes. It is valid in all of the objects that allow data input (transactions and procedures), both with Win and Web interface. It is supported by the .NET, C/SQL, Visual Basic, Visual Fox Pro and Java languages, and all database handlers, except for dbf.

How can I verify if the property is being considered?
As we said earlier, this property is valid for creation and reorganization, which means that in the creation/reorganization impact analysis, warnings are displayed when the auto-number property is ignored.
When the property is assigned to a non-primary-key field, the message is AutoNumbe=True ignored. Attribute %1 is not table %2's primary key.
It also warns if it is not implemented in the database handler, in which case the message is: AutoNumber=True ignored for attribut %1. Autonumbering is not supported in this DBMS.

How can the new key's value be obtained when releasing records in a procedure?
By having a transaction with the following structure:

AttId*
AttDsc
where AttId is N(6) and has the auto-number property in True, and a procedure with the code:

new
Attdsc = &Attdsc
endnew

In order to obtain the key number, the AttId attribute must be referenced immediately after the EndNew attribute. Keep in mind that this may affect the procedure's browsing.

How is it implemented?
Not all the DBMS provide the same support in order to implement this feature. The implementation's detailed information for each of the handlers may be useful for database administrators; refer to the Release Notes.

Example
You can check out an example at
http://www.gxopen.com.uy/hproject.asp?122 

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