frappe-syntax-controllers

Frappe controller validation uses lifecycle hooks like before_validate or validate to check item rows and calculate totals. Proper hook-order awareness ensures calculations execute correctly before database commits without causing recursive saves.

The best way to override ERPNext DocType controllers is applying override classes, mixins, or document events. This extension pattern customizes existing logic while maintaining safe super calls and preserving base Frappe behavior.

Use db_set in Frappe document events when you need to update fields after save or submit without triggering recursive lifecycle hooks. Standard assignment is safer during validation phases where normal save flows handle database commits.

Yes, this approach supports Frappe v14 through v16 by applying version-aware controller patterns. It handles differences in naming rules, flags, and post-save behavior across versions to ensure document events remain compatible.

To reverse side effects on cancel, implement the on_cancel lifecycle hook in your Frappe document controller. This hook executes cleanup logic to undo submit actions, ensuring database consistency when documents are cancelled.

Frappe controller recursion happens when save or db_set calls are placed incorrectly inside validation or before_save hooks. Avoid this by using flags to control flow and ensuring post-save logic does not re-trigger the document event lifecycle.