Develop and Test Code
Language essentials
Know X++ classes, interfaces, inheritance with extends and implements, access modifiers, static members, delegates and events. Know select syntax: while select with joins, firstonly, forupdate, order by and aggregates, plus the set-based statements insert_recordset, update_recordset and delete_from that replace row-by-row loops.
Transactions and errors
A logical unit of work is ttsbegin, validation, writes, ttscommit. An exception thrown inside the block rolls the transaction back. Use throw error for fatal conditions, checkFailed for validation messages that should not abort the flow, and Info log for information. Catching an exception without rethrowing hides failures.
Testing
Unit tests extend SysTestCase; each test method is public and decorated with SysTestMethod. Set up data in the test, assert with the framework methods, and clean up. Automated UI regression uses RSAT driven by Task recorder, and the Acceptance Test Library provides reusable test building blocks.
Performance-aware code
Avoid a select inside a loop, filter on indexed fields in index order, use temporary tables (InMemory or TempDB) and RecordInsertList for bulk work, and avoid forupdate when not updating because it takes row locks.
Trap: committing inside a catch block, validating outside the transaction, or decorating a test method that is not public. Rule of thumb: one transaction per unit of work, no user interaction inside it, and never a database call inside a loop you can express as a set-based statement.