has_and_belongs_to_many关联已更改时的Rails模型回调

Question

I'm trying to fire an after_save callback on my Job model only when it has a Surveyor added or changed on it (given that one is also present too).

# app/models/job.rb 
has_and_belongs_to_many :surveyors
after_save :send_mail, if: ->(r) { r.surveyor_ids_changed? and r.surveyor_ids.present? }

# app/models/surveyor.rb
has_and_belongs_to_many :jobs

# permitted parameters on job
:job_name, :job_address, surveyor_ids: []

How might I change the model callback to get the send_mail method firing properly?

Answer 1

#changed? will always be false after saving the model, but you can use #previous_changes to do the thing