Pull data from multiple tables in Rails - sql

Question

I am new in Ruby on Rails and I am trying to make a book registration website. Everything works fine except category section. When a user assign a category to his book, my database copies book_categories.id and put it in book.book_categories_id. The website also have a profile page, where you can view user's book(s). My problem is to display a category.name, I searched a lot of similar problems but I have not found the right answer.
Here is my book controller:
before_action :set_book, except: [:index, :new, :create]
before_action :authenticate_user!, except: [:show]
def show
#photos = #book.photos
end
def index
#books = current_user.books
end
def new
#book = current_user.books.build
end
def create
#book = current_user.books.build(books_params)
if #book.save
redirect_to listing_book_path(#book), notice: "Saved."
else
flash[:alert] = "Failed."
render :new
end
end
private
def set_book
#book = Book.find(params[:id])
end
def book_params
params.require(:book).permit(:book_categories_id, :book_name, :summary, :address, :price, :company_name)
end
As long as I understand, I have to allow my controller to have access to my category table but I do not know how. Also, all of my categories store in seed.rb.
This is my BookCategory.rb model:
class BookCategory < ActiveRecord::Base
has_many :books, :foreign_key => :book_categories_id
end
Book.rb model:
class Book < ApplicationRecord
belongs_to :user, :foreign_key => 'user_id'
has_many :photos, dependent: :delete_all
validates :book_name, presence: true
validates :book_categories_id, presence: true
def cover_photo
if self.photos.length > 0
self.photos[0].image.url
else
"default/image-default.jpg"
end
end
end
My schema.rb:
create_table "book_categories", force: :cascade do |t|
t.string "name"
t.string "subcategory"
t.text "description"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "book", force: :cascade do |t|
t.string "book_name"
t.text "summary"
t.string "address"
t.decimal "price", precision: 8, scale: 2
t.boolean "active"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "user_id"
t.float "latitude"
t.float "longitude"
t.string "company_name"
t.integer "book_categories_id"
t.index ["book_categories_id"], name: "index_books_on_book_categories_id"
end
Usually, when I type #book_categories.name, I get an error:
undefined method `name' for nil:NilClass
And at the very end, it says Parameters: {"id"=>"15"} whereas the category.id is different, and it passes book.id instead.
What I am doing wrong?

Answer 1

First fix the naming problem you have going. I don't know how the books table got called "book" instead of "books" in the schema, but you might have to fix that first.
Then category should be singular everywhere except the database table name. You need to make a migration to fix the foreign key and its index in the books table something like this:
class FixCategoryNaming < ActiveRecord::Migration
def change
remove_column :books, :book_categories_id
add_reference :books, :book_category, index: true, foreign_key: true
end
end
Then run rails db:migrate and check the schema looks ok
Then in the BookCategory class change the line to simply
has_many :books
You need to add this line to your Book class
belongs_to :book_category
and change the validation for book_category to be this
validates :book_category_id, presence: true
Then in the view for book index you have a #books variable. You can get the book name and category name for each book like this:
<% #books.each do |book| %>
<p><%= book.book_name %></p>
<p><%= book.book_categories.name %></p>
<% end %>

Answer 2

I think you need to setup as has_many through relationship. This is a good place to start http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association