Check box filters

check_box_filter.rb

scope :category_query, ->(query) do
  if query.count == 1
    joins(:article_categories).where('article_categories.category_id': query.first)
  else
    joins(:article_categories).
    where('article_categories.article_id': ArticleCategory.select('article_categories.article_id')
                                                          .where(category_id: query)
                                                          .group('article_categories.article_id')
                                                          .having("COUNT(article_categories.article_id) > #{query.count - 1}"))
    .uniq
  end
end