ruby-on-rails - 传递对象或对象 ID？

Question

给定以下代码，哪种enroll方法更好，为什么？还是应该以其他方式完全改进此代码？

我对上述“更好”的想法基本上可以归结为 1) 哲学上最正确(最佳实践)和 2) 最高效/性能最好。

Class Course < ActiveRecord::Base
  has_many :enrollments # basically a join table
  has_many :students, :source => :user, :through => :enrollments
  def enroll_this_way(student)
    self.enrollments << Enrollment.new(:course_id => self.id, :student_id => student.id)
  end
  # OR
  def enroll_that_way(student_id)
    self.enrollments << Enrollment.new(:course_id => self.id, :student_id => student_id)
  end
end

Answer 1

def enroll_this_way(student)
  self.enrollments.build :student => student
end