What is the order of ActiveRecord callbacks and validations?
The most-up-to-date version of this list for the latest version of Rails can be found in the ActiveRecord::Callbacks documentation. The lists for Rails 4, 3 & 2 are below.
Rails 4
The most up-to-date version of this list can be found in the Rails 4 Guides.
Creating an object
before_validationafter_validationbefore_savearound_savebefore_createaround_createafter_createafter_saveafter_commit/after_rollback
Updating an object
before_validationafter_validationbefore_savearound_savebefore_updatearound_updateafter_updateafter_saveafter_commit/after_rollback
Destroying an object
before_destroyaround_destroyafter_destroyafter_commit/after_rollback
Rails 3
The most up-to-date version of this list can be found in the Rails 3 Guides.
Creating an object
before_validationafter_validationbefore_savearound_savebefore_createaround_createafter_createafter_save
Updating an object
before_validationafter_validationbefore_savearound_savebefore_updatearound_updateafter_updateafter_save
Destroying an object
before_destroyaround_destroyafter_destroy
Rails 2
The most up-to-date version of this list can be found in the Rails 2.3 Guides
Creating an object
before_validationbefore_validation_on_createafter_validationafter_validation_on_createbefore_savebefore_createINSERToperationafter_createafter_save
Updating an object
before_validationbefore_validation_on_updateafter_validationafter_validation_on_updatebefore_savebefore_updateUPDATEoperationafter_updateafter_save
Destroying an object
before_destroyDELETEoperationafter_destroy
Since you need to first validate the reference_code, the assign_reference method can be called in the after_validation callback or any callback appearing after it in the list I provided above.
Rails 5
Here is a list with all the available Active Record callbacks, listed in the same order in which they will get called during the respective operations:
1 Creating an Object
before_validationafter_validationbefore_savearound_savebefore_createaround_createafter_createafter_saveafter_commit/after_rollback
2 Updating an Object
before_validationafter_validationbefore_savearound_savebefore_updatearound_updateafter_updateafter_saveafter_commit/after_rollback
3 Destroying an Object
before_destroyaround_destroyafter_destroyafter_commit/after_rollback
after_save runs both on create and update, but always after the more specific callbacks after_create and after_update, no matter the order in which the macro calls were executed.
before_destroy callbacks should be placed before dependent: :destroy associations (or use the prepend: true option), to ensure they execute before the records are deleted by dependent: :destroy.