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.
class Movie < Base
attr_json :movie_id, :integer
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.
Step 2. Create a view for page editing
<!-- app/views/spina/admin/parts/movies/_form.html.erb -->
<label class="block text-sm leading-5 font-medium text-gray-700"><%= f.object.title %></label>
<%= f.select :movie_id, Movie.all.pluck(:name, :id) %>
Step 3. Register your new part
In an initializer, register your newly created part so you can use it in your theme:
Step 4. 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