Chapter 6: Nested Resources

In this chapter, you'll add Comments as a nested resource under Posts.

What are Nested Resources?

Nested resources are resources that belong to a parent resource. In our blog:

• Comments belong to Posts
• The URL reflects this: /admin/blogging/posts/1/blogging/comments
• Comments are automatically scoped to their parent post

Generating the Comment Resource

rails generate pu:res:scaffold Comment body:text user:belongs_to Blogging/Post:belongs_to --dest=blogging

Setting Up the Association

Update the Post model to add the has_many association:

# packages/blogging/app/models/blogging/post.rb
class Blogging::Post < Blogging::ResourceRecord
  belongs_to :user
  has_many :comments, foreign_key: :post_id, dependent: :destroy
  # ... existing code
end

The Comment Model

The generator creates:

# packages/blogging/app/models/blogging/comment.rb
class Blogging::Comment < Blogging::ResourceRecord
  belongs_to :user
  belongs_to :post, class_name: "Blogging::Post"
  # ... generated code
end

Note: When referencing resources within the same package, the generator uses the short name (:post) while setting the appropriate class_name and foreign key to the correct table.

Connecting to the Portal

Connect comments to the admin portal:

rails generate pu:res:conn Blogging::Comment --dest=admin_portal

Because Comment has belongs_to :post, Plutonium automatically creates nested routes:

• GET /admin/blogging/posts/:blogging_post_id/blogging/comments
• POST /admin/blogging/posts/:blogging_post_id/blogging/comments
• GET /admin/blogging/posts/:blogging_post_id/blogging/comments/:id

Showing Comments on Post Detail

To show a comments panel on the post detail page, add comments to permitted_associations in the policy:

# packages/blogging/app/policies/blogging/post_policy.rb
class Blogging::PostPolicy < Blogging::ResourcePolicy
  def permitted_associations
    %i[user comments]
  end
end

The panel links to the nested comments route and shows "Add Comment" if the user has permission.

Comment Policy

Add authorization for comments:

# packages/blogging/app/policies/blogging/comment_policy.rb
class Blogging::CommentPolicy < Blogging::ResourcePolicy
  def read?
    true # Anyone can read comments
  end

  def create?
    true # Anyone authenticated can comment
  end

  def update?
    owner?
  end

  def destroy?
    owner? || post_owner?
  end

  # Scope to comments on published posts (or user's own posts)
  def relation_scope(relation)
    relation.joins(:post).where(
      blogging_posts: {published: true}
    ).or(
      relation.where(user_id: user.id)
    )
  end

  private

  def owner?
    record.user_id == user.id
  end

  def post_owner?
    record.post.user_id == user.id
  end
end

Nested Forms

You can edit comments directly on the post form using nested attributes:

# In Post model
accepts_nested_attributes_for :comments, allow_destroy: true

# In PostDefinition - option 1: inline block
nested_input :comments do |definition|
  definition.input :body
end

# In PostDefinition - option 2: use existing definition
nested_input :comments, using: Blogging::CommentDefinition, fields: %i[body]

This adds an inline comments editor to the post form.

Nesting Limitations

Plutonium supports one level of nesting. For deeper hierarchies (e.g., Replies to Comments), keep URLs flat: /blogging/comments/:blogging_comment_id/blogging/replies

What's Next

Our blog has posts and comments. In the next chapter, we'll create an Author Portal to show how multiple portals can share resources with different access levels.

Continue to Chapter 7: Creating an Author Portal →