A video can have multiple categories.

video.rb 
has_many :video_categories
has_many :categories, through: :video_categories

category.rb
has_many :video_categories
has_many :videos, through: :video_categories

I have this simple form that allows the user to select the categories he wants to combine in order to find specific videos. For example, there's a "python" category and "advanced" category. If he selected these two categories, it should show videos that has both categories.

Video A - Categories [1,4,7] (this is the categories ids)

Video B - Categories [1,2,7,9]

Video C - Categories [7,9]

If the user select the categories [1,7], the output should be video A and B. The current scope that I have its returning ALL videos that has category 1, ALL videos that has category 7 and videos that has BOTH of them.

I want just the videos that has BOTH of them. How do I do that ?

Current scope:

video.rb
scope :for_categories, -> (category_ids) {
    joins(:video_categories).where(
      video_categories: { category_id: category_ids }
    )
  }

pages_controller.rb
def search
 @results = Video.for_categories(params[:category_ids])
end

My form

        <%= form_with url: "/search", method: :get do |form| %>
            <%= form.collection_check_boxes(:category_ids, Category.all,
                :id, :title, { prompt: 'None'}, { multiple: true} ) do |cat| %>
              <label class="text-capitalize checkbox-inline mr-2">
                <%= cat.check_box %>
                <%= cat.label %>
              </label>
            <% end %>
          <%= form.submit "Search" %>
        <% end %>

CodePudding user response：

I was able to find the solution with the following code

video.rb
scope :by_categories, -> (category_ids) {
    joins(:categories).where(categories: [category_ids] )
  }

  scope :by_all_categories, -> (category_ids) {
    by_categories(category_ids).
    group("videos.id").
    having('count(videos.id) >= ?', category_ids.size)
  }
pages_controller.rb
def search
    @results = Video.by_all_categories(params[:category_ids].reject(&:empty?))
end

CodePudding user response：

You want apply a GROUP and use HAVING to set a condition on the group to ensure that the number of categories joined matches the number of ids:

class Video
  def self.for_categories(*category_ids)
     ids = category_ids.flatten # handles a single array as input
     group(:id)
       .joins(:categories)
       .where(categories: { id:  ids })
       .having(
          Category.arel_table[:id]
                  .count
                  .gteq(ids.length)
       )
  end
end

In terms of SQL this will give you something like:

SELECT videos.*
FROM videos
INNER JOIN video_categories ON video_categories.video_id = videos.id
INNER JOIN categories ON video_categories.category_id = categories.id
WHERE categories.id IN (1, 2, 3)
GROUP BY videos.id
HAVING COUNT(categories.id) >= 3