[RUBY] [Rails] Implementation of tagging function using intermediate table (without Gem)


Select multiple checkboxes and implement the tagging function via the intermediate table.

Development environment

・ Ruby: 2.5.7 Rails: 5.2.4 ・ Vagrant: 2.2.7 -VirtualBox: 6.1 ・ OS: macOS Catalina

E-R diagram

スクリーンショット 2020-12-21 10 58 14 The above image is the image to be implemented this time. This time, I will talk about an example of selecting and registering multiple types of saunas that I have implemented.

Advance preparation

We have prepared a screen to create a new sauna like the one in the image. In this talk, we will use the `method of selecting multiple checkboxes in the sauna genre and implementing it using the sauna genre, which is an intermediate table. I will talk about basic functions such as registration function on the assumption that they have already been implemented. スクリーンショット 2020-12-21 11 07 41

Describe the association in the model


class Sauna < ApplicationRecord
  has_many :sauna_genres, dependent: :destroy
  has_many :genres, through: :sauna_genres


class SaunaGenre < ApplicationRecord
  belongs_to :genre
  belongs_to :sauna


class Genre < ApplicationRecord
  has_many :sauna_genres
  has_many :saunas, through: :sauna_genres



  def create
    @sauna = Sauna.new(sauna_params)
    @sauna.user_id = current_user.id
    if @sauna.save
      redirect_to user_sauna_path(@sauna)
      render 'new'


   def sauna_params
      genre_ids: []

genre_ids: [] allows multiple checkbox values ​​to be passed as an array.


  <%=f.label :genre_ids, "Genre function" %>
    <% Genre.all.each do |genre| %>
      <%= f.check_box :genre_ids, 
         { multiple: true, checked: @sauna.genres.find_by(id: genre.id).present?, 
         include_hidden: false }, genre[:id] %>
       <label class="form-check-label">
         <%= genre.name %>
     <% end %>

form.check_box: label_ids → As the value of params,"label_ids" => ["1", "2", "3"]You can send a value with a hash key in this way. You can send parameters for multiple checkboxes in an array format by using the multiple option. checked: @ task.labels.find_by (id: label.id) .present? This is to check the label registered on the edit screen etc. include_hidden: false → This method does not send parameters for items that are not registered.

*** If you implement it as it is, you can create multiple intermediate tables at first glance, and I thought that there is no problem because it is checked firmly when editing ***, but even if you uncheck all the checks on the edit screen and update it, the genre Multiple names did not disappear. What is the cause? With this implementation method, nil will be returned as a value if you send it empty ***. *** *** To solve it, we will devise a little strong parameter.



  def sauna_params
    values = params.require(:sauna).permit(
      genre_ids: []
    if values[:genre_ids].nil?
      values[:genre_ids] = [] 
    return values

By doing this, I was able to create something that does not have a genre by sending an empty array to genre_ids when nil is returned. As long as I'm making a genre, I don't think there is no genre, but I noticed it, so I'll leave it as a memorandum.

Thank you very much

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