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Railsで前後のレコードを取得したいとき

More than 3 years have passed since last update.

例えば、グループなどに投稿された記事の詳細で「次へ」や「前へ」などのボタンを付けたかったのですが、若干悩んでしまったのでまとめておきたいと思います。

記事の一覧のコントローラをこんなに感じにします。

app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def index(group_id)
    @group = Group.find(group_id)
    @posts = @group.posts.order('published_at desc, id desc')
  end
end

Postモデルにメソッドを追加します。

app/models/post.rb
class Interview < ActiveRecord::Base
  belongs_to :group

  def previous
    group.posts.order('published_at desc, id desc').where('published_at <= ? and id < ?', published_at, id).first
  end

  def next
    group.posts.order('published_at desc, id desc').where('published_at >= ? and id > ?', published, id).reverse.first
  end  

あとは、ビューでモデルのメソッドを呼びます。

<%= link_to '前へ', group_post(@group, @post.previous) if @post.previous %>
<%= link_to '次へ', group_post(@group, @post.next) if @post.next %>
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