Friendly_id using value from belongs_to association

问题

I have the following models:

class User < ActiveRecord::Base
  extend FriendlyId
  friendly_id :first_name, :use => :slugged

  has_one :professor
  after_create :create_professor

  def create_professor
    self.professor = Professor.create 
  end

end 

class Professor < ActiveRecord::Base
  extend FriendlyId
  friendly_id :first_name, :use => :slugged

  belongs_to :user
  def first_name
    user.first_name 
  end

end

At the time that create_professor is called and therefore the execution passes to the Professor model (self.professor = Professor.create), when it gets to try to create the slug in this method:

def first_name
  user.first_name 
end

I get an undefined method first_name for nil:NilClass, so it seems the Professor object doesn't know what is his associated user.

Any tips on how to solve this?

回答1:

You don't need:

  def create_professor
    self.professor = Professor.create 
  end

Since create_professor is created by your association.

来源：https://stackoverflow.com/questions/11488700/friendly-id-using-value-from-belongs-to-association