How to find Books that belong to desired Categories with Rails?

how_to.rb

# The logic here is dishonestly stolen from Gutentag gem:
# https://github.com/pat/gutentag/blob/0dbcd1dbcd4de8930e589cf964498abe46127a98/lib/gutentag/tagged_with/query.rb#L11

# Models definitions

class Book < ApplicationRecord
  has_many :category_mappings, as: :categorizable, dependent: :destroy
  has_many :categories, through: :category_mappings 
end

class CategoryMapping < ApplicationRecord
  belongs_to :category
  belongs_to :categorizable, polymorphic: true
end

class Category < ApplicationRecord
  has_many :category_mappings, dependent: :restrict_with_error
end

# Let's assume we want to find books that belong to all categories below,
# i.e. every book belongs to "Detective" AND "Fiction" categories.
searched_categories = %w[Detective Fiction]

# The most important part where magic happens.
sub_query = 
  CategoryMapping 
    .joins(:category)
    .select(:categorizable_id)
    .where(categorizable_type: Book.base_class.name)
    .where(Category.table_name => { name: searched_categories })
    .group(:categorizable_id)
    .having("COUNT(*) = #{searched_categories.size}")
    .to_sql

books_table_id = "#{Book.quoted_table_name}.#{Book.quoted_primary_key}"

# Resulting query that returns desired Books
Book.where("#{books_table_id} IN (#{sub_query})")