★Rails Turtorial：ステータスフィード

[yuyanegishi]

def home
    if logged_in?
      @micropost  = current_user.microposts.build
      @feed_items = current_user.feed.paginate(page: params[:page])
    end
end

def feed
    following_ids = "SELECT followed_id FROM relationships
                     WHERE follower_id = :user_id"
    Micropost.where("user_id IN (#{following_ids})
                     OR user_id = :user_id", user_id: id)
end

<% if logged_in? %>
  <div class="row">
    <aside class="col-md-4">
      <section class="user_info">
        <%= render 'shared/user_info' %>
      </section>
      <section class="stats">
        <%= render 'shared/stats' %>
      </section>
      <section class="micropost_form">
        <%= render 'shared/micropost_form' %>
      </section>
    </aside>
    <div class="col-md-8">
      <h3>Micropost Feed</h3>
      <%= render 'shared/feed' %>
    </div>
  </div>
<% else %>
  <div class="center jumbotron">
    <h1>Welcome to the Sample App </h1>

    <h2>
      This is the home page for the
      <a href="https://railstutorial.jp/">Ruby on Rails Tutorial</a>
      sample application.
    </h2>

    <%= link_to "Sign up now!", signup_path, class: "btn btn-lg btn-primary" %>
  </div>

  <%= link_to image_tag("rails.png", alt: "Rails logo"), 'http://rubyonrails.org/' %>
<% end %>

<% if @feed_items.any? %>
  <ol class="microposts">
    <%= render @feed_items %>
  </ol>
  <%= will_paginate @feed_items %>
<% end %>

内容

following_ids = "SELECT followed_id FROM relationships WHERE follower_id = :user_id"

• relationshipsテーブルから、follower_idがuser_idと一致するレコードのfollower_idを抽出する。

リファレンスの確認　※スッキリわかるSQL入門

• SELECT 列名 FROM テーブル名 （WHERE 修飾）

内容

Micropost.where("user_id IN (#{following_ids}) OR user_id = :user_id", user_id: id)

• relationshipsテーブルから、follower_idがuser_idと一致するレコードのfollower_idを抽出する。

リファレンスの確認　※スッキリわかるSQL入門、Ruby on Rails API

where(opts = :chain, *rest)

Returns a new relation, which is the result of filtering the current relation according to the conditions in the arguments.

where accepts conditions in one of several formats. In the examples below,
the resulting SQL is given as an illustration; the actual query generated may be different depending on the database adapter.

[yuyanegishi]

Micropost.where("user_id = 1")   

=>#<ActiveRecord::Relation [#<Micropost id: 303, content: "テストテスト", user_id: 1, created_at: "2018-11-29 06:08:08", updated_at: "2018-11-29 06:08:08", picture: nil>, #<Micropost id: 295, content: "Ipsa voluptatem modi et a omnis.", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 289, content: "Commodi aut quam optio ipsum in aut voluptas reici...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 283, content: "Ducimus eos repudiandae labore quia dolorem sit.", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 277, content: "Nostrum accusamus ullam ut ducimus praesentium non...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 271, content: "Et et veritatis repudiandae voluptatibus unde labo...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 265, content: "Eos doloribus quisquam itaque quam sed autem accus...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 259, content: "Veniam aspernatur voluptate deserunt in repellendu...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 253, content: "Nisi ipsam optio officia quidem tenetur in corpori...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, #<Micropost id: 247, content: "Fugiat vel deleniti quos corporis quo consectetur ...", user_id: 1, created_at: "2018-11-22 01:14:29", updated_at: "2018-11-22 01:14:29", picture: nil>, ...]>