通过关系从has-many-u获取连接模型

要么我不理解你的问题,要么你会惊讶这是多么明显。 您将这样定义关系:

#coffee_drinker.rb
has_many :cups
has_many :coffees, :through => :cup

#cup.rb
belongs_to :coffee
belongs_to :coffee_drinker

#coffee.rb
has_many :cups
has_many :coffee_drinkers, :through => :cup

coffee_drinker.cups
coffee_drinker.coffees

coffee.cups
coffee.coffee_drinkers

#coffee_drinker.rb
after_save :update_cups_drunk

def update_cups_drunk
  cups.find_by_coffee_id(coffee_id).increment!(:count)
end

#maybe you don't have access to the coffee_id

def update_cups_drunk
  cups.find_by_coffee_id(coffees.last.id).increment!(:count)
end