Files to look at:

• frmMain.cs (VB: frmMain.vb)
• SequenceGenerator.cs (VB: SequenceGenerator.vb)

This is a general solution, showing how to use the ExplicitUnitOfWork class to generate sequential numbers that can then be used as user-friendly identifiers in documents, as invoice line numbers, etc. The ExplicitUnitOfWork class is used to ensure that the assignment of the sequential number will be a part of a database transaction that results in the successful saving of the document.
Hence, the current solution will also work in a scenario with high-volume of concurrency transactions.

See also:
XAF: How to generate and assign a sequential number for a business object within a database transaction, while being a part of a successful saving process (XAF)