在@subject = Subject.find(params[:subject_id])中找不到没有ID的主题

Question

我有一个错误:在@subject = Subject.find(params:subject_id)中找不到没有ID的Subject

我建立了多到多的联系。有三种模式:教师模式、学科模式和订阅模式。订阅模型包括以下字段: teacher_id和subject_id。

class Subject < ActiveRecord::Base
  has_many :subscriptions
  has_many :teacher, :through => :subscriptions
end

class Teacher < ActiveRecord::Base
  has_many :subscriptions
  has_many :subjects, :through => :subscriptions
end

class Subscription < ActiveRecord::Base
  belongs_to :subject
  belongs_to :teacher
end

teacher_controller

def create
        @subject = Subject.find(params[:subject_id])
                @teacher = Teacher.new(teacher_params)
                respond_to do |format|
                  @teacher.subjects << @subject
                  if @teacher.save
        format.html { redirect_to @teacher, notice: 'Teacher was successfully created.' 
        format.json { render action: 'show', status: :created, location: @teacher }
      else
        format.html { render action: 'new' }
        format.json { render json: @teacher.errors, status: :unprocessable_entity }

      end

    end

    end

_form.html.erb

  <%= form_for(@teacher,:html => { class: 'login-form' })  do |f| %>

    <%= f.fields_for :subject do |n| %>
                <%= n.select(@subject, @subjects.map{|p| [p.name, p.id]}) %>
                <% end %>
    ...
<% form %>


resources :teachers do
    resources :subjects
end

Answer 1

代之而行

def create
  @subject = Subject.where("id =?", params[:subject_id]).first
  unless @subject.blank?
    @teacher = Teacher.new(teacher_params)
    ......
    ......
  else
    # set flash message and redirect
  end
end

Answer 2

在视图_form.html.erb中，替换select_tag

<%= select_tag "subject_id", options_from_collection_for_select(@subjects, "id", "name") %>

在控制器代码中，

def create
  @subject = Subject.where(id: params[:subject_id]).first

  if @subject.present?
    #YOUR CODE GOES HERE.
  else
    render 'new' # OR render to the action where your teacher form resides
  end
end