Outer Join on an Association in ActiveRecord

activerecord_outer_join.rb

class Project < ActiveRecord::Base
  has_and_belongs_to_many :phrases
end

class Phrase < ActiveRecord::Base
  has_and_belongs_to_many :projects
end


join_dependency = ActiveRecord::Associations::JoinDependency.new(Project, [:phrases], [])
manager = Arel::SelectManager.new(Phrase)
join_dependency.join_associations.each do |assoc|
  assoc.join_type = Arel::OuterJoin
  assoc.join_to(manager)
end

# SELECT `phrases`.* FROM `phrases`
#  LEFT OUTER JOIN `phrases_projects` ON `phrases_projects`.`project_id` = `projects`.`id`
#  LEFT OUTER JOIN `phrases` ON `phrases`.`id` = `phrases_projects`.`phrase_id`"
Phrase.joins(manager.join_sources).to_sql