CODEWITHSUNDEEP
ruby-on-railsrubyhas-many-through
Babi Hannah
Babi Hannah

Reputation: 21

How to show a list of elements using a join table

I have three tables, one of which is a many-to-many relationship table:

class Category < ApplicationRecord
  has_many :categorizations
  has_many :products, :through => :categorizations
end

class Product < ApplicationRecord
  has_many :categorizations, dependent: :destroy
  has_many :categories, :through => :categorizations
end

and the table Categorizations:

class Categorization < ApplicationRecord
  belongs_to :category
  belongs_to :product
end

I saved the categories ids in a array:

  def product_params
    params.require(:product).permit(:name_product, :hallmark, :description, :image_url, :price, category_ids:[])
  end

In new.html.erb:

  <% Category.all.each do |category| %>
   <label>
      <%= check_box_tag "product[category_ids][]", category.id, field.object.categories.include?(Category) %>
      <%= category.name_category %>
   </label>
  <%end%>

I can't display the category names. In show.html.erb I tried everything, but it only displays the ID of the categories in which the product belongs.

How do I display the category names? In the database I can do a JOIN, but in Ruby on Rails it is difficult.

Upvotes: 2

Views: 255

Answers (1)

Ilya Lavrov
Ilya Lavrov

Reputation: 2860

It does not able in Rails to store a relation in an array column. You may load necessary categories and make access by category id.

# for single product
category_ids = product.category_ids
# for many products
category_ids = products.flat_map(&:category_ids)

# load categories
categories = Category.where(id: category_ids).index_by(&:id)
# the result structure 
# {1 => #<Category id: 1, ...>, 2 => #<Category id: 2, ...> ... }

# now all related categories preloaded
products.each do |product|
  product.category_ids.each do |category_id|
    puts categories[category_id]
  end
end

Upvotes: 0

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