Conditionally displaying resources in a many-to-many relationship - Rails 4 - ruby-on-rails

Question

Working through my first Rails app. It will be used for searching and viewing data on books within certain categories.
Two resources: Categories and Books. I created a many-to-many HMT (has many through) relationship (following this RailsCast), as each category will have many books and each book will belong to more than one category. Here's the relevant controller code:
Category model (category.rb)
class Category < ActiveRecord::Base
has_ancestry
has_many :categorizations
has_many :books, :through => :categorizations
end
Book model (book.rb)
class Book < ActiveRecord::Base
has_many :categorizations
has_many :categories, :through => :categorizations
accepts_nested_attributes_for :categories
end
Join model (categorization.rb)
class Categorization < ActiveRecord::Base
belongs_to :book
belongs_to :category
end
And here's the database schema:
schema.rb
create_table "books", force: true do |t|
t.string "title"
t.string "url"
t.integer "rank_overall"
t.integer "rank_category"
t.decimal "price"
t.integer "reviews"
t.decimal "rating"
t.date "published"
t.string "img_cover"
t.string "author"
t.datetime "created_at"
t.datetime "updated_at"
t.string "asin"
t.integer "length"
end
create_table "categories", force: true do |t|
t.string "name"
t.text "content"
t.string "ancestry"
t.datetime "created_at"
t.datetime "updated_at"
end
add_index "categories", ["ancestry"], name: "index_categories_on_ancestry", using: :btree
create_table "categorizations", force: true do |t|
t.integer "book_id"
t.integer "category_id"
t.integer "rank"
t.datetime "created_at"
t.datetime "updated_at"
end
add_index "categorizations", ["book_id"], name: "index_categorizations_on_book_id", using: :btree
add_index "categorizations", ["category_id"], name: "index_categorizations_on_category_id", using: :btree
I have a show view that shows each category. In this view I'd like to show the books that are in each corresponding category. I have these simple loops:
.col-1-3
%strong TITLE
%ul
- #books.each do |book|
%li= book.title
.col-1-3
%strong AUTHOR
%ul
- #books.each do |book|
%li= book.author
.col-1-3
%strong ULR
%ul
- #books.each do |book|
%li= book.url
And in my category model I have the following:
def show
#books = Book.order("title").includes(:categorizations).select("books.*")
end
def book_params
params.require(:book).permit(:books => [{:title => [:book_id]}, {:id => [:category_id]}, :author, :url] )
end
Here's the problem, from the loops in my view I'm receiving information from all the books (ie: titles, authors, and urls of all the books in the database) and I only want that from the books that are in that particular category.
I believe I need to change the logic in my categories_controller.rb, is this correct? I realize that I'm selecting all the books .select("books.*") but I don't know how to edit this to conditionally call only the books that match the category of that being displayed in the show view.
Grateful for insights.
Update:
Realized that this information is also quite helpful. When assigning categories to books (upon book creation) I use this code:
= check_box_tag "book[category_ids][]", category.id, #book.category_ids.include?(category.id), id: dom_id(category)
Perhaps it's possible to somehow reference dom_id(category) inside of the category model?
Forgive my "newbishness." I'm a front-end guy who is only now beginning to really venture into the back-end.

Answer 1

One possible solution is to change the show action in categories like this
#books=Category.find(params[:id]).books
Assuming the :id param is the id for the category (which would be the convention if you are in the categories controller).
If you don't need the information about the category and you only need the books, you could do a join (not a include) with categorizations and use a where like categorizations: {category_id: params[:id]}. That's not as clear as the 1st option, but it saves a query if you are not showing info about the category.