HABTM join

habtm.rb

%w(Charger Escalade Cooper Viper Taurus Impala).each do |car|
  Car.create(name: car)
end

%w(Aircon Rack Sunroof Rims 4WD).each do |feature|
  Feature.create(name: feature)
end

aircon = Feature.where(name: 'Aircon').first
rack = Feature.where(name: 'Rack').first
sunroof = Feature.where(name: 'Sunroof').first
rims = Feature.where(name: 'Rims').first
four = Feature.where(name: '4WD').first

charger = Car.where(name: 'Charger').first
escalade = Car.where(name: 'Escalade').first
cooper = Car.where(name: 'Cooper').first
viper = Car.where(name: 'Viper').first
taurus = Car.where(name: 'Taurus').first
impala = Car.where(name: 'Impala').first

charger.cars_features.create(feature_id: aircon.id)
charger.cars_features.create(feature_id: rack.id)

escalade.cars_features.create(feature_id: aircon.id)
escalade.cars_features.create(feature_id: sunroof.id)
escalade.cars_features.create(feature_id: four.id)

cooper.cars_features.create(feature_id: rack.id)
cooper.cars_features.create(feature_id: rims.id)

viper.cars_features.create(feature_id: sunroof.id)

taurus.cars_features.create(feature_id: sunroof.id)
taurus.cars_features.create(feature_id: rims.id)

impala.cars_features.create(feature_id: aircon.id)
impala.cars_features.create(feature_id: rims.id)

Car.joins(:features).where(features: {id: [rims.id]}).uniq.all.map(&:name)
# => ["Escalade"]

Car.joins(:features).where(features: {id: [four.id]}).uniq.all.map(&:name)
# => ["Escalade"]

Car.joins(:features).where(features: {id: [sunroof.id]}).uniq.all.map(&:name)
# => ["Escalade", "Viper", "Taurus"]