How to setup relation so I can add multiple associations to self?

Question

I have two classes

class Project < ActiveRecord::Base
  has_many :related_projects
  has_many :projects, through: :related_projects
end

class RelatedProject < ActiveRecord::Base
  belongs_to :project
  belongs_to :related_project, class_name: 'Project', foreign_key: 'related_project_id'
end

RelatedProject is the association table that stores projects that are related to each other. Essentially project has a many-to-many relation to itself.

What I can't figure out is how to set this up so I can say something like

project.project_ids = [2,3] which would update a project to have two related projects. It should automatically add the association on save. This works fine if I am not doing a many to many relationship to the same model.

What am I missing?

Answer 1

If I understand you correctly, I think you need to use has_and_belongs_to_many which will create a many to many association table. This will essentially replace your RelatedProject model.

Look at the docs for that relation.