Rails subcategories - ruby-on-rails

Question

How do I find and manage subcategories? (the find_subcategory method i'd defined does not seem to work.)
class CategoriesController < ApplicationController
before_action :find_category, only: [:show]
def index
#categories = Category.order(:name)
end
def show
end
private
def find_category
#category = Category.find(params[:id])
end
def find_subcategory
#subcategory = Category.children.find(params[:parent_id])
end
end
I'm using the acts_as_tree gem, which has:
root = Category.create("name" => "root")
child1 = root.children.create("name" => "child1")
subchild1 = child1.children.create("name" => "subchild1")
root.parent # => nil
child1.parent # => root
root.children # => [child1]
root.children.first.children.first # => subchild1

Answer 1

It's not clear what you want your find_subcategory method to do, but if you want it to find all subcategories of the category with id in params[:id], then change it to
def find_subcategories
#subcategories = Category.where(:parent_id => params[:parent_id]).all
end
In your original you're just looking for a single subcategory, and if you just want a single category you might as well just load it from it's id.

Answer 2

I know you accepted the answer, but I've done this before and so it might be beneficial to explain how we did it:
Firstly, we used the ancestry gem. I think acts_as_tree is deprecated -- acts_as_tree is better than ancestry, I forgot why we used it now - ancestry works in a very similar way (parent column, child methods, etc).
I'll explain our implementation with ancestry - hopefully it will give you some ideas for acts_as_tree:
#app/models/category.rb
class Category < ActiveRecord::Base
has_ancestry #-> enables the ancestry gem (in your case it should be "acts_as_tree"
end
This will allow you to populate the ancestry (in your case parent_id) column in your categories model, and (most importantly) gives you the ability to call the child methods attached to objects in the model:
#category.parent
#category.children
... etc.
--
The important thing to note here is how we're able to call the child objects (which would be subcategories in your case).
Your method is to create separate objects and have them inherit from each other. The beauty of ancestry / acts_as_tree is their added methods.
Any object with the correct parent ids can call their "children" as associative data:
In our case, we were able to associate all the objects using the ancetry column. This is slightly trickier than acts_as_tree because you have to provide the entire hierarchy in the column (which is lame), nonetheless the result is still the same:
#app/controllers/categories_controller.rb
class CategoriesController < ApplicationController
def index
#categories = Category.all
end
end
#app/views/categories/index.html.erb
<%= render #categories %>
#app/views/categories/_category.html.erb
<%= category.name %>
<%= render category.children if category.has_children? %>
This will output the sub categories for you:
How do I find and manage subcategories
You can do it like this:
#subcategories = Category.where parent_id: #category.id
or if you have your ancestry set up properly, you should be able to use the following:
#config/routes.rb
resources :categories
#app/controllers/categories_controller.rb
class CategoriesController < ApplicationController
def show
#category = Category.find params[:id]
end
end
This will allow you to use:
#app/views/categories/show.html.erb
<% #category.children.each do |subcategory| %>
<%= subcategory.name %>
<% end %>