Recursive many to many relationship on Rails - mysql

Question

For my project, I have some Post linked to Category. What I want to achieve, is to have Category who are relatives to others. Like this :
c1 = Category.create(name: 'Television')
c2 = Category.create(name: 'TV')
c1.relatives << c1
I use a join table :
create_table :category_relative, id: false do |t|
t.belongs_to :category_1
t.belongs_to :category_2
end
add_index :category_relative, [:category_1_id, :category_2_id]
So far, I have tried this :
class Category < ActiveRecord::Base
has_and_belongs_to_many :relatives, class_name: 'Category',
join_table: 'category_relative', foreign_key: 'category_1_id',
association_foreign_key: 'category_2_id'
end
This is working, but only in a single way :
c1.relatives
=> []
c2.relatives
=> [#<Category:0x007fcc610b8418 id: 1, name: 'Television']
I know that I can add a relative for each entry, but this is too heavy for my database :
c1.relatives << c2
c2.relatives << c1
Do you have any idea ? Should I write the JOIN manually ?

Answer 1

You can try something like this
class Category < ActiveRecord::Base
has_many :category_relatives, dependent: :destroy
has_many :relatives, :through => :category_relative
has_many :inverse_category_relatives, :class_name => "categoryRelative", :foreign_key => "category_2_id", dependent: :destroy
has_many :inverse_relatives, :through => :inverse_category_relative, :source => :category
end
Through class:
class CategoryRelative < ActiveRecord::Base
belongs_to :category
belongs_to :relative, :class_name => "Category"
end
With this code you have a many to many relationship between the same class thourgh another