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Nested records when creating

A lot of you asked for the ability to create nested has_many records on the New view. Although it's fairly "easy" to implement using accepts_nested_attributes_for for simple cases, it's a different story to extract it, make it available, and cover most edge cases for everyone. That's why Avo and no other similar gems dont't offer this feature as a first-party feature. But, that doesn't mean that it's impossible to implement it yourself. It's actually similar to how you'd implement it for your own app.

We prepared this scenario where a Fish model has_many Reviews. I know, it's not the Slider has_many Items example, but you'll get the point.

Full set of changes

The full code is available in Avo's dummy app and the changes in this PR.

Guide to add it to your app

You can add this functionality using these steps.

1. Add accepts_nested_attributes_for on your parent model

ruby
class Fish < ApplicationRecord
  has_many :reviews, as: :reviewable

  accepts_nested_attributes_for :reviews
end

WARNING

Ensure you have the has_many association on the parent model.

2. Add a JS helper package that dynamically adds more review forms

yarn add stimulus-rails-nested-form

In your JS file register the controller.

js
// Probably app/javascript/avo.custom.js
import { Application } from '@hotwired/stimulus'
import NestedForm from 'stimulus-rails-nested-form'

const application = Application.start()
application.register('nested-form', NestedForm)

INFO

Use this guide to add custom JavaScript to your Avo app.

3. Generate a new resource tool

bin/rails generate avo:resource_tool nested_fish_reviews

This will generate two files. The NestedFishReviews ruby file you'll register on the FishResource file and we'll edit the template to contain our fields.

4. Register the tool on the resource

We'll display it only on the New view.

ruby
class FishResource < Avo::BaseResource
  # other fields actions, filters and more

  field :reviews, as: :has_many

  tool NestedFishReviews, only_on: :new
end

5. Create a partial for one new review

This partial will have the fields for one new review which we'll add more on the page.

erb
<!-- app/views/avo/partials/_fish_review.html.erb -->
<%= render Avo::PanelComponent.new do |c| %>
  <% c.body do %>
    <div class="nested-form-wrapper divide-y" data-new-record="<%= f.object.new_record? %>">
      <%= avo_edit_field :body, as: :trix, form: f, help: "What should the review say", required: true %>
      <%= avo_edit_field :user, as: :belongs_to, form: f, help: "Who created the review", required: true %>
    </div>
  <% end %>
<% end %>

6. Update the resource tool partial

It's time to put it all together. In the resource tool partial we're wrapping the whole thing with the nested-form controller div, creating a new form helper to reference the nested fields with form.fields_for and wrapping the "new" template so we can use replicate it using the nested-form package. In the footer we'll also add the button that will add new reviews on the page.

erb
<!-- app/views/avo/resource_tools/_nested_fish_reviews.html.erb -->
<div class="flex flex-col">
  <%= content_tag :div,data: { controller: 'nested-form', nested_form_wrapper_selector_value: '.nested-form-wrapper' } do %>
    <%= render Avo::PanelComponent.new(name: "Reviews", description: "Create some reviews for this fish") do |c| %>
      <% c.bare_content do %>
        <% if form.present? %>
          <template data-nested-form-target="template">
            <%= form.fields_for :reviews, Review.new, multiple: true, child_index: 'NEW_RECORD' do |todo_fields| %>
              <%= render "avo/partials/fish_review", f: todo_fields %>
            <% end %>
          </template>
          <div class="space-y-4">
            <%= form.fields_for :reviews, Review.new, multiple: true do |todo_fields| %>
              <%= render "avo/partials/fish_review", f: todo_fields %>
            <% end %>
            <div data-nested-form-target="target"></div>
          </div>
        <% end %>
      <% end %>
      <% c.footer_tools do %>
        <div class="mt-4">
          <%= a_link 'javascript:void(0);', icon: 'plus', color: :primary, style: :outline, data: {action: "click->nested-form#add"} do %>
            Add another review
          <% end %>
        </div>
      <% end %>
    <% end %>
  <% end %>
</div>

7. Permit the new nested params

There's one more step we need to do and that's to whitelist the new reviews_attributes params to be passed to the model.

ruby
class FishResource < Avo::BaseResource
  self.extra_params = [reviews_attributes: [:body, :user_id]]

  # other fields actions, filters and more

  field :reviews, as: :has_many

  tool NestedFishReviews, only_on: :new
end

Conclusion

There you have it!

Apart from the resource tool and the extra_params attribute, we wrote regular Rails code that we would have to write to get this functionality in our app.