创建嵌套资源的新方法时出错

  resources :flows do
    resources :fmodules
  end

fmodules控制器中的新方法:

# /flows/1/fmodules/new
def new
    @flow = Flow.find(params[:flow_id])
    @fmodule = @flow.fmodules.build
end

模型:

class Flow < ApplicationRecord
    has_many :fmodules, dependent: :destroy
    validates :code, presence: true, length: { maximum: 5 }
    validates :name, presence: true
end

class Fmodule < ApplicationRecord
    belongs_to :flow
end

/flows/1/fmodules/new ruby说 unknown attribute 'flow_id' for Fmodule.

我不知道怎么了

此外,这是Fmodel的迁移

class CreateFmodules < ActiveRecord::Migration[5.1]
  def change
    create_table :fmodules do |t|
      t.string :code
      t.string :name
      t.string :f_code

      t.timestamps
    end
    add_foreign_key :fmodules, :flows, column: :f_code
  end
end