Custom parts

All page content is stored in a single JSONB-column in the database. Spina uses the attr_json gem to work with these nested json objects. All default parts are AttrJson::Model objects. Follow the steps below to create your own custom part.

Step 1. Create a part

Let's imagine our app contains a movie database. We'd like to add a part to select one of the movies in our collection. First we need to create the object that can be stored as page content.

# app/models/spina/parts/movie.rb
module Spina
  module Parts
    class Movie < Base
      attr_json :movie_id, :integer

      def content
        Movie.find_by(id: movie_id)
      end

    end
  end
end

In this simplified example we make the content method do a query and return a Movie record. Beware of N+1 queries if you go this route. Generally, the more you store directly in JSON, the better your performance.

Any ActiveRecord::RecordNotFound Exception will be displayed as 404, which may be happening when using Movie.find (movie_id) if movie_id is nil or not found in Database. You should consider using Movie.find_by (id: movie_id), which will not throw an Error but return nil if movie_id is nil or not found in Database.

Step 2. Create a view for page editing

<!-- app/views/spina/admin/parts/movies/_form.html.erb -->
<div class="mt-6">
  <label class="block text-sm leading-5 font-medium text-gray-700"><%= f.object.title %></label>
  <div class="mt-1">
    <%= f.select :movie_id, Movie.all.pluck(:name, :id) %>
  </div>
</div>

Step 3. Register your new part

In an initializer, register your newly created part so you can use it in your theme:

Rails.application.reloader.to_prepare do
  Spina::Part.register(Spina::Parts::Movie)
end

Step 4. View template example

<p>Film Director: <%= content(:movie)[:director] %></p>

Step 5. Go wild

Of course, this is a very simple example. You can store a lot this way. You can take a look at the existing parts in Spina for inspiration. If you want to learn more, you can also take a look at the attr_json readme.