在创建时使用来自子记录的信息更新 rails 父记录

Question

this is my first post so I'm not exactly sure how to format this. Lmk if I'm doing anything wrong.

I'm fairly new to rails and I am making an app that basically just allows users to submit 'grimes' (which you can think of as reviews) for other users. The app has two basic models: users and grimes.

User Model:

class User < ApplicationRecord
    has_many :grimes
end

Grimes Model:

class Grime < ApplicationRecord
  belongs_to :user
  validates :user, presence: true
end

each grime has a griminess attribute, which is basically the rating from 1-5 for the grime. Each user also has a griminess attribute, which I would like to be the sum of the griminess of each of a user's associated grimes. ie. if user1 has two grimes, g1 with griminess 3 and g2 with griminess 2, then user1 griminess should be 5.

I could do this by iterating through each of the user's grimes when I would like to display the user's griminess, but that seems very unnecessary. Instead, I would like to just increment the user's griminess each time a new grime associated with them is added, but I can't figure out how to do that right now.

the form to create a grime looks like this:

<%= form_for @grime do |f| %>
    Title: <%= f.text_field :title %><br />
    Description: <%= f.text_area :description %><br />
    Griminess Level:  <%= f.select :griminess, (0..5) %>
    Select Grimer: <%= f.collection_select(:user_id, User.all, :id, :name) %><br />
    <%= f.submit %>
<% end %> 

and my grimes#create looks like this:

def create
      @grime = Grime.new(grime_params)
      
      if @grime.save
          flash[:success] = "Grime Saved Successfully"
          redirect_to @grime
      else
          flash[:error] = "Error: Could Not Save Grime!"
          render :new
      end
  end

I feel like I should be able to do something like @grime.user.griminess += @grime.griminess in the create method, but that doesn't seem to work for me. Can anyone recommend a better way to approach this?

Answer 1

Add after_save hook in Grime which will call a method on a grime whenever that grime is saved.

class Grime < ApplicationRecord
  after_save :update_user_griminess # register the callback
  belongs_to :user
  validates :user, presence: true

  #callback body
  def update_user_griminess
    user.griminess = user.grimes.sum(:griminess) # update user griminess as sum of it's all grimes' griminess 
    user.save
  end      
end

There is an alternative after_create hook in ActiveRecord which runs just once when the object is created for the first time, but I preferred after_save here to adjust for cases when a grime 's griminess is updated.