mildmojo · April 5, 2024 16:00 · chochkov · Aug 14, 2014 · araslanov-e · Dec 4, 2015
diff --git a/left_join_arel_example.rb b/left_join_arel_example.rb
 # Here's a contrived example of a LEFT JOIN using ARel. This is an example of
 # the mechanics, not a real-world use case.

 # NOTE: In the gist comments, @ozydingo linked their general-purpose ActiveRecord
 # extension that works for any named association. That's what I really wanted!
 # Go use that! Go: https://gist.github.com/ozydingo/70de96ad57ab69003446

 # == DEFINITIONS
 # - A Taxi is a car for hire. A taxi has_many :passengers.
 # - A Passenger records one person riding in one taxi one time. It belongs_to :taxi.

 class Taxi < ActiveRecord::Base
  # This scope LEFT JOINs the Passenger table. You might use this if you wanted
  # to select taxis by a set of taxi and passenger IDs (as with the
  # SQL "taxis.id IN () OR passengers.id IN ()").
  def self.left_join_passengers
    taxis = Taxi.arel_table
    passengers = Passenger.arel_table

    # The key here is providing the join type (Arel::Nodes::OuterJoin) and
    # grabbing the ARel join object itself from Arel::SelectManager#join_sources
    # to feed to ActiveRecord's #joins method.
    # SQL equivalent: "LEFT OUTER JOIN passengers ON taxis.id = passengers.taxi_id"
    taxi_passengers = taxis.join(passengers, Arel::Nodes::OuterJoin).
                            on(taxis[:id].eq(passengers[:taxi_id])).
                            join_sources
    joins(taxi_passengers)
  end
 end

 # Sources that almost documented this:
 # http://blog.donwilson.net/2011/11/constructing-a-less-than-simple-query-with-rails-and-arel/
	# Here's a contrived example of a LEFT JOIN using ARel. This is an example of
	# the mechanics, not a real-world use case.

	# NOTE: In the gist comments, @ozydingo linked their general-purpose ActiveRecord
	# extension that works for any named association. That's what I really wanted!
	# Go use that! Go: https://gist.github.com/ozydingo/70de96ad57ab69003446

	# == DEFINITIONS
	# - A Taxi is a car for hire. A taxi has_many :passengers.
	# - A Passenger records one person riding in one taxi one time. It belongs_to :taxi.

	class Taxi < ActiveRecord::Base
	# This scope LEFT JOINs the Passenger table. You might use this if you wanted
	# to select taxis by a set of taxi and passenger IDs (as with the
	# SQL "taxis.id IN () OR passengers.id IN ()").
	def self.left_join_passengers
	taxis = Taxi.arel_table
	passengers = Passenger.arel_table

	# The key here is providing the join type (Arel::Nodes::OuterJoin) and
	# grabbing the ARel join object itself from Arel::SelectManager#join_sources
	# to feed to ActiveRecord's #joins method.
	# SQL equivalent: "LEFT OUTER JOIN passengers ON taxis.id = passengers.taxi_id"
	taxi_passengers = taxis.join(passengers, Arel::Nodes::OuterJoin).
	on(taxis[:id].eq(passengers[:taxi_id])).
	join_sources
	joins(taxi_passengers)
	end
	end

	# Sources that almost documented this:
	# http://blog.donwilson.net/2011/11/constructing-a-less-than-simple-query-with-rails-and-arel/