[Rails] Sort the post list by date or number of likes using the pull-down box

At the beginning

I wanted a function to sort posts by date and time and the number of likes in the original application, so I managed to implement it while being quite addicted, so I will leave it as a memorandum.

Premise

__ ● Environment __ ・ Ruby 2.6 series ・ Rails 5.2 series __ ● Library used __ ・ Slim ・ Devise __ ● Like function is implemented __ ・ [Rails] Implementation of Like Function (Slim and devise are also introduced in this article)

↓ It looks like this after mounting ↓

(I'm sorry it doesn't look good ...) ezgif.com-video-to-gif.gif

Implementation

1. First, create a pull-down form

h1 post list 　 = form_with model: @post, url: search_path, method: :get, local: true do |form| = form.select :keyword, [ ['Posts are newest', 'new'], ['Posts oldest', 'old'], ['In descending order of likes', 'likes'], ['In ascending order of likes', 'dislikes'], ] = form.submit 　 #================The part that was originally implemented========================

@posts.each do |post| p = link_to post.user.email, user_path(post.user.id) br = link_to post.title, post_path(post.id) br = post.created_at br
- if user_signed_in?
  - if post.favorited_by?(current_user) = link_to "How nice: #{post.favorites.count}", post_favorites_path(post.id), method: :delete
  - else = link_to "How nice: #{post.favorites.count}", post_favorites_path(post.id), method: :post
- else = post.favorites.count #================The part that was originally implemented========================



 >> __ ・ Let's break down what is happening. __

>>```ruby
= form_with model: @post, url: search_path, 
            method: :get, local: true do |form|

__-The `Post model` is specified as the model used in the form. This will send the data with the value params [: post]. __

__ ・ After searching, we will prepare a page for displaying search results, so set the path to `` `search_path``` and send it as a GET request. __

__ ・ local: true. If this is not specified in form_with, it will be considered as Ajax communication. If you do not use JS, you must add it or it will not be rendered. __

= form.select :keyword, [ ['Posts are newest', 'new'], ['Posts oldest', 'old'], ['In descending order of likes', 'likes'], ['In ascending order of likes', 'dislikes'], ] = form.submit



 >> __ ・ You can create a pull-down form by using the select method.
 The usage is like `` `select (" object "," method "," choice ")` ``. __

 >> __ ・ ``` The first argument object``` corresponds to the `` `post object` ``, but omit it when using form_with. __

 >> __ ・ ``` The second argument method``` is a` `thing that is sent as a parameter to the` `controller, so please describe it freely. __
 __ In this case, since keyword is specified, it will be sent as `` `params [: keyword]` ``. __

 >> __ ・ In the choice``` part, which is the third argument,
　```[ [Value to be displayed by pull-down 1,Parameters sent to the action], 
　[Value to be displayed in the pull-down part 2,Parameters sent to the action], 
 [Value to be displayed in pull-down, Part 1, Parameter sent to action]] Specify `` `. __

### 2. Edit the routing

>```ruby:config/routes.rb
Rails.application.routes.draw do
#================The part that was originally implemented========================
  devise_for :users
  resources :users
　
  root to: 'posts#index'
  resources :posts, only: [:index, :new, :create, :show, :edit, :update] do
    resource :favorites, only: [:create, :destroy]
  end
#================The part that was originally implemented========================
　
  #Send search results to the search action of the posts controller
+ get 'search' => 'posts#search'
　
end

3. Edit the posts controller

class PostsController < ApplicationController . . . def search selection = params[:keyword] @posts = Post.sort(selection) end . . . end


 >> __ ・ Create a search action. In params [: keyword], the value selected in the sort form is received and stored in a local variable called selection. __
　
 >> __ ・ `sort` is an instance method for Post. After that, define the Post model class so that posts will be retrieved in the order of sorting by the value of selection. __

### 4. Define the sort instance method in the Post model.

>```ruby:app/models/user.rb
class Post < ApplicationRecord
  .
  .
  .
  def self.sort(selection)
    case selection
    when 'new'
      return all.order(created_at: :DESC)
    when 'old'
      return all.order(created_at: :ASC)
    when 'likes'
      return find(Favorite.group(:post_id).order(Arel.sql('count(post_id) desc')).pluck(:post_id))
    when 'dislikes'
      return find(Favorite.group(:post_id).order(Arel.sql('count(post_id) asc')).pluck(:post_id))
    end
  end
  .
  .
  .
end

__ ・ Since it is an instance method definition, self is added. __

__ ・ The case statement defines the conditions for sorting according to the value passed to selection. __

__ ↓ Sort by date __

when 'new' return all.order(created_at: :DESC) when 'old' return all.order(created_at: :ASC)


 >> __ ↓ Sort by number of likes __

>>```ruby
when 'likes'
   return find(Favorite.group(:post_id).order(Arel.sql('count(post_id) desc')).pluck(:post_id))
when 'dislikes'
   return find(Favorite.group(:post_id).order(Arel.sql('count(post_id) asc')).pluck(:post_id))

__ · Favorite.group (: post_id) will group posts with the same post_id. __

__ · order (Arel.sql ('count (post_id) desc')), count how many user_ids are stored in grouped posts and sort from the most (that is, how much I'm counting if it's liked). __ __ʻArel.sql () is a SQL injection countermeasure`. __

__ ・ In pluck (: post_id), post_id itself is acquired. If you do not describe this, the find corresponding to the call to Post will not be found and an error will occur. __

_ * Currently, the problem that posts with 0 likes are not displayed is not supported. I'm sorry…. I will add it as soon as it is resolved. _

5. Display the view of search results

h1 search results 　 = form_with url: search_path, method: :get, local: true do |form| = form.select :keyword, [ ['Posts are newest', 'new'], ['Posts oldest', 'old'], ['In descending order of likes', 'likes'], ['In ascending order of likes', 'dislikes'], ] = form.submit

@posts.each do |post| p = link_to post.user.email, user_path(post.user.id) br = link_to post.title, post_path(post.id) br = post.created_at br
- if user_signed_in?
  - if post.favorited_by?(current_user) = link_to "How nice: #{post.favorites.count}", post_favorites_path(post.id), method: :delete
  - else = link_to "How nice: #{post.favorites.count}", post_favorites_path(post.id), method: :post
- else = post.favorites.count


 >> __ ・ Create a setatch.html.slim file in the app / views / posts directory and describe it as above. __
　
 >> __ ・ The content described here is exactly the same as the content described in posts / index.html.slim, so it will be partialized. __

### 6. Partial view

 > #### __6-1. Partialization of search form __

>```ruby:app/views/posts/_select_form.html.slim
= form_with model: @post, url: search_path, method: :get, local: true do |form|
  = form.select :keyword, [ ['Posts are newest', 'new'],
                            ['Posts oldest', 'old'],
                            ['In descending order of likes', 'likes'],
                            ['In ascending order of likes', 'dislikes'],
                          ]
  = form.submit

__ · Create a _select_form.html.slim file in the app / views / posts directory and port the entire pull-down menu code. __

__6-2. Partialization of post list & search result list __

@posts.each do |post| p = link_to post.user.email, user_path(post.user.id) br = link_to post.title, post_path(post.id) br = post.created_at br
- if user_signed_in?
  - if post.favorited_by?(current_user) = link_to "How nice: #{post.favorites.count}", post_favorites_path(post.id), method: :delete
  - else = link_to "How nice: #{post.favorites.count}", post_favorites_path(post.id), method: :post
- else = post.favorites.count


 >> __ ・ Create a `_result.html.slim` file in the app / views / posts directory and port the entire code for displaying the post list. __

 > #### __6-3. Render to each view __

>```ruby:app/views/posts/index.html.slim
h1 post list
　
= render 'select_form'
　
= render 'result'

h1 search results 　 = render 'select_form' 　 = render 'result'


#### that's all.


## Finally
 This completes the sort function implementation!
 To be honest, I'm not confident in many parts, so I'd be very happy if you could tell me anything wrong!

## Article that I was very helpful
 [How to implement search function without gem? Supports multiple tables! ](Https://prokyou.com/rails/nogemsearch/)
 [[Rails] How to use select to create a select box with a complete understanding form](https://310nae.com/rails-selectbox/)
[select (ActionView::Helpers::FormOptionsHelper) - APIdock](https://apidock.com/rails/ActionView/Helpers/FormOptionsHelper/select)