Rails 4 - How to set db attribute on create - ruby-on-rails

Question

This seems like a dumb question, but how do I update a database field from a model method? The incident.incident_number value is displayed on all the forms and emails, but is NULL in the database:
incident.rb
validate :incident_number, :on => :save
def incident_number
(self.created_at.strftime("%Y") + self.created_at.to_date.jd.to_s + self.id.to_s).to_i
end
incidents_controller.rb
def create
#incident = Incident.new(incident_params)
#incident.user_id = current_user.id
#incident.state_id = 1
respond_to do |format|
if #incident.save
IncidentMailer.new_incident_notification(#incident).deliver
format.html { redirect_to my_incidents_path, notice: 'Incident was successfully created.' }
format.json { render action: 'show', status: :created, location: #incident }
else
format.html { render action: 'new' }
format.json { render json: #incident.errors, status: :unprocessable_entity }
end
end
end

Answer 1

Your current method doesn't persist to the database, it just runs the logic every time the method is called.
There are a number of ways to do this - either via write_attributes (works well in before_save)
before_save :update_incident_number, if: Proc.new { conditional_logic_here }
...
def update_incident_number
write_attribute(:incident_number, new_value)
end
Or, use update_attribute(s)
after_commit :update_incident_number, if: Proc.new { conditional_logic }
...
def update_incident_number
self.update_attribute(:incident_number, new_value)
end
There are a few ways to skin this cat, try a few and see which you prefer based on what callbacks are triggered, and how they deal with your record / changed properties.