Rails STI form components conditional by type

blog_post.rb

# app/models/blog_post.rb
class BlogPost < Post
  has_many :comments
end

comment.rb

# app/models/comment.rb
class Comment < ActiveRecord::Base

end

news_post.rb

# app/models/news_post.rb
class NewsPost < Post

end

post.rb

# app/models/post.rb
class Post < ActiveRecord::Base
  def self.types
    %w(BlogPost NewsPost)
  end

  validates :name, presence: true
  validates :slug, presence: true
end

posts-_form.html.erb

# app/views/posts/_form.html.erb
<%= form_for(@post.becomes(Post)) do |f| %>
  <% if @post.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2>

      <ul>
      <% @post.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :type %><br>
    <%= f.select :type, Post.types %>
  </div>
  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </div>
  <div class="field">
    <%= f.label :slug %><br>
    <%= f.text_field :slug %>
  </div>

  <%= render_view_component(@post, :form, form: f) %>

  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

posts-blog_posts-_show_components.html.erb

# app/views/posts/blog_posts/_show_components.html.erb
<h4>Comments</h4>
<p>
  There are <%= post.comments.count %> comments.
</p>

posts-news_posts-_form_components.html.erb

# app/views/posts/news_posts/_form_components.html.erb
<div class="field">
  <%= form.label :published_at %><br>
  <%= form.datetime_select :published_at %>
</div>

posts-news_posts-_show_components.html.erb

# app/views/posts/news_posts/_show_components.html.erb
<p>
  <strong>Published at:</strong>
  <%= post.published_at.to_s(:short) %>
</p>

posts-show.html.erb

# app/views/posts/show.html.erb
<p id="notice"><%= notice %></p>

<p>
  <strong>Type:</strong>
  <%= @post.type %>
</p>

<p>
  <strong>Name:</strong>
  <%= @post.name %>
</p>

<p>
  <strong>Slug:</strong>
  <%= @post.slug %>
</p>

<%= render_view_component(@post) %>

<%= link_to 'Edit', edit_post_path(@post) %> |
<%= link_to 'Back', posts_path %>

posts_helper.rb

# app/helpers/posts_helper.rb
module PostsHelper
  def render_view_component(post, component_name = action_name, locals = {})
    return unless post_view_component_exists?(component_name, post)

    render(
      partial: post_view_component_name(component_name, post),
      locals: locals.merge(post: post)
    )
  end

  private

  def post_view_component_exists?(component_name, post)
    lookup_context.exists?(post_view_component_name(component_name, post), [], partial: true)
  end

  def post_view_component_name(component_name, post)
    "posts/#{post.class.name.demodulize.pluralize.underscore}/#{component_name}_component"
  end
end

schema.rb

ActiveRecord::Schema.define(version: 20150418093537) do

  create_table "comments", force: :cascade do |t|
    t.string   "content"
    t.integer  "blog_post_id"
    t.datetime "created_at",   null: false
    t.datetime "updated_at",   null: false
  end

  create_table "posts", force: :cascade do |t|
    t.string   "type"
    t.string   "name"
    t.string   "slug"
    t.datetime "created_at",   null: false
    t.datetime "updated_at",   null: false
    t.datetime "published_at"
  end

end