I want to create a form to select the [Rails] category

Hello. I'm currently building a bulletin board in Rails.

I wanted to classify the threads on the bulletin board by category and display them, so I implemented it with the intention of selecting the category when creating threads.

I've started to touch Rails recently, so if you are familiar with it, please ask Masakari.


Ruby 2.5 Rails 5.1

DB / preparation

Designed with many threads tied to a category スクリーンショット 2020-07-09 12.08.06.png

Don't forget to set between models ...


class Thread < ApplicationRecord
	belongs_to :category


class Category < ApplicationRecord
	has_many :threads

First, register the category

It won't start without a category, so let's register. You can use it from the console, but I think I'll add more categories in the future, so I'll create a registration form. After registering, you will be taken to the list page.

First, write routes and controller



Rails.application.routes.draw do
  root 'thread#index'
  resources :thread #I also write thread routing
  resources :categories



class CategoriesController < ApplicationController
	def new
		@category = Category.new

	def create
		@category = Category.new(category_params)
		if @category.save
			redirect_to categories_path, notice: "Has registered"
			render :new

	def index
		@categories = Category.all

	def category_params

スクリーンショット 2020-07-09 12.26.28.png


<div class="col-sm-12">
	<h2 class="text-center">Add category</h2>
	<%= form_with model: @category, local: true do |f| %>
		<div class="form_input">
			<%= f.label :name %>
			<%= f.text_field :name, class:"form-control" %>
		<div class="form_action row">
			<%= f.submit "sign up", class: "btn col-sm-12 submit_btn" %>
	<% end %>

--List page

スクリーンショット 2020-07-09 12.28.24.png

I wish I could display this for the time being


	<% @categories.each do |category| %>
		<%= category.name %>
	<% end %>

Create a thread submission form

Now that you've registered, you'll be able to select a category on the thread's post form.



class ThreadsController < ApplicationController
  def new
    @thread = Thread.new

  def create
    @Thread = Thread.new(board_params)
    if @thread.save
      redirect_to thread_path(@thread), notice: "Post has been completed"
      render :new

  def show
    @thread = Thread.find(params[:id])

  def board_params

--Posting page

スクリーンショット 2020-07-09 12.36.23.png

You can create a selection form with collection_select.

As for how to use it, I use it like this ... collection_select (object name, method name, array of elements, value attribute item, text item [, option or HTML attribute or event attribute])

In this example, Category.all corresponds to the" array of elements "part. Perhaps, rather than writing Category.all, put it in a variable on the controller and use it in view. It may be better to have a shape like that.

It would be helpful if someone could point out here.


<div class="col-sm-12">
	<h2 class="text-center">Make a thread</h2>
	<%= form_with model: @thread, local: true do |f| %>
		<div class="form_input">
			<%= f.label :title %>
			<%= f.text_field :title, class: "form-control" %>
		<div class="form_input">
			<%= f.label :body %>
			<%= f.text_area :body, class: "form-control" %>
		<div class="form_input">
			<%= f.label :category_id %>
			<%= f.collection_select :category_id, Category.all, :id, :name,
															:include_blank => "Please select a category" %>
		<div class="form_action row">
			<%= f.submit "Post", class: "btn col-sm-12 submit_btn" %>
	<% end %>

You will be able to select as follows.

スクリーンショット 2020-07-09 12.37.45.png

in conclusion

Thank you for watching until the end. I will write a lot of articles from now on, and I will output more and more.

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