Rails counter cache with has_many: :through

Question

I have a Part model that has_many :images, through: :gallery and I would like to implement counter_cache to store the images count of a part. This is my setup.

Part

has_one :gallery, dependent: :destroy
has_many :images, through: :gallery

Gallery

belongs_to :part
has_many :images

Image

belongs_to :gallery

I can do @part.images to fetch images of a part and now I would like to cache images count so I can do @part.images.size or even order parts by images_count. I would normally do this using counter_cache: true on a belongs_to side but how do I do this in this case? Is it possible?

How about those answers - https://stackoverflow.com/questions/8991118/has-many-through-with-counter-cache ? The problem is similar to yours — Paweł Dąbrowski, Nov 11 '19 at 12:48
Thanx, the second answer in that thread helped me solve this problem. — jedi, Nov 11 '19 at 13:08

score 0 · Answer 1 · answered Nov 11 '19 at 13:10

0

Based on the answer from the comment I managed to solve it by doing it like this:

add images_count column to Parts and update counters in the migration

class AddImagesCountToParts < ActiveRecord::Migration[5.1]
  def change
    add_column :parts, :images_count, :integer, default: 0, null: false

    Part.find_each { |part| Part.reset_counters(part.id, :images) }
  end
end

add counter_cache: :images_count to Gallery

belongs_to :part, counter_cache: :images_count

answered Nov 11 '19 at 13:10

jedi

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That will just count the galleries. – max Nov 12 '19 at 01:08
No. I verified this, `part.images.size == part.images_count` – jedi Nov 13 '19 at 14:04

Rails counter cache with has_many: :through

1 Answers1