嵌套模型引发未定义的方法错误

我一直在跟踪 RailsCast 197 尝试这种嵌套的模型/表单,并且在这段代码上花了2个多小时的时间破解了我的头,但是没有用。我忽略了什么?

我有以下型号:

class Workout < ActiveRecord::Base
  belongs_to :user
  has_many :performed_exercises, :dependent => :destroy
  accepts_nested_attributes_for :performed_exercises
end

class PerformedExercise < ActiveRecord::Base
  belongs_to :workout
  belongs_to :exercise
  has_many :performed_sets, :dependent => :destroy
  accepts_nested_attributes_for :performed_sets
end

class PerformedSet < ActiveRecord::Base
  belongs_to :performed_exercise
end

在我的WorkoutController中,我有以下功能:

  def new
    # We only need to build one of each since they will be added dynamically
    @workout = Workout.new
    @workout.performed_exercises.build
    @workout.performed_exercises.performed_sets.build
  end

当我运行测试并在浏览器中调用控制器时,会得到以下错误:

undefined method `performed_sets' for #<Class:0x7f6ef6fa6560>

提前感谢你的帮助-我的错误不再让我惊讶!

编辑 : fflyer05:我尝试使用与RailsCast相同的代码对集合进行迭代,并尝试在已执行的\练习[0]上构建已执行的\集,但它不起作用。执行其他操作时,会得到一个未初始化的常量PerformedExercise::PerformedSet错误