How would one go about eager loading a categories collection's root categories? #337

Activity

1. pugsiman

   changed the title [-]How would one go about eager loading a categories collection's root categories[/-] [+]How would one go about eager loading a categories collection's root categories?[/+] on Nov 14, 2018
2. fizvlad commented on Jun 15, 2022

   

   fizvlad

   on Jun 15, 2022

   More actions

   (The question is 4 years, yeeeeah 🐧)

   While solving similar problem, I've ended up using association through scenic view

   I have created an SQL view which looked something like this:

   SELECT
       DISTINCT ON (descendant_id)
       ancestor_id AS root_id,
       descendant_id AS leaf_id,
       generations AS depth
   FROM category_hierarchies
   ORDER BY descendant_id, generations DESC

   Then I defined a read-only model which uses this view:

   # frozen_string_literal: true
   
   class CategoryRootHierarchy < ApplicationRecord
     self.primary_key = nil
   
     belongs_to :leaf, class_name: 'Category'
     belongs_to :root, class_name: 'Category'
   
     def readonly?
       true
     end
   end

   ... and added an association to category model:

   # frozen_string_literal: true
   class Category < ApplicationRecord
     has_closure_tree order: :code, name_column: :code, dependent: :destroy
   
     has_many :items, dependent: :nullify
     has_one :root_hierarchy, class_name: 'CategoryRootHierarchy', foreign_key: 'leaf_id', inverse_of: :leaf
   end

   After that I was able to preload the root category:

   Item.includes(category: [{ root_hierarchy: [:root] }])

   ---

   This is probably can be done on Rails level with use of ancestor_hierarchies association, but it will probably look scarier