Question

因此，我的作业要求我生成一个页面来处理学生，课程和部分。我应该使用many_to_many或类似的方法来列出所有共享数据。我的具体问题是，我创建了一个似乎无效的新表（rails g scaffold enrolling students：references section：references）。当我尝试使用学生和部分创建新的注册时，出现错误，指出“部分必须存在” error。我不知道这个错误是从哪里来的。此视图中的sections字段仅填充有现有的部分，因此它说“必须存在”的事实非常令人困惑。谁能指出我正确的方向来解决这个问题？我已经尝试过不同的方法来重建这个项目3次，只是...卡住了。我将发布相关代码，但是如果我对您可能需要查看的部分有误，我会很乐意发布其余部分。

class Enrollment < ApplicationRecord
belongs_to :section
belongs_to :student 
end

<%= form_with(model: enrollment, local: true) do |form| %>
<% if enrollment.errors.any? %>
<div id="error_explanation">
  <h2><%= pluralize(enrollment.errors.count, "error") %> 
prohibited this enrollment from being saved:</h2>

  <ul>
  <% enrollment.errors.full_messages.each do |message| %>
    <li><%= message %></li>
  <% end %>
  </ul>
 </div>
 <% end %>

<div class="field">
<%= form.label :student_id %>
<%= form.collection_select :student_id, Student.order(:student_name), :id, 
:student_id, include_blank:true %>
</div>

<div class="field">
<%= form.label :course_id %>
<%= form.collection_select :course_id, Course.order(:name), :id, :name, 
include_blank: true %>
</div>

<div class="field">
<%= form.label :sections_number %>
<%= form.collection_select :section_number, Section.all, :id, 
:section_number, include_blank:false %>
</div>

<div class="actions">
<%= form.submit %>
</div>
<% end %>

class Section < ApplicationRecord
has_many :enrollments
has_and_belongs_to_many :students, through: :enrollments       
belongs_to :course

def numsem
    "#{course.name} #{course_id}"
end
end

L

-----------------------编辑添加控制器代码----------------

class EnrollmentsController < ApplicationController
before_action :set_enrollment, only: [:show, :edit, :update, :destroy]

# GET /enrollments
# GET /enrollments.json
def index
@enrollments = Enrollments.all
end

# GET /enrollments/1
# GET /enrollments/1.json
def show
end

# GET /enrollments/new
def new
@enrollment = Enrollments.new
@sections = Section.all
@students = Student.all
end

# GET /enrollments/1/edit
def edit
end

# POST /enrollments
# POST /enrollments.json
def create
@enrollment = Enrollments.new(enrollment_params)

respond_to do |format|
  if @enrollment.save
    format.html { redirect_to @enrollment, notice: 'Enrollments was 
successfully created.' }
    format.json { render :show, status: :created, location: @enrollment }
   else
    format.html { render :new }
    format.json { render json: @enrollment.errors, status: 
 :unprocessable_entity }
  end
 end
 end

# PATCH/PUT /enrollments/1
# PATCH/PUT /enrollments/1.json
def update
respond_to do |format|
  if @enrollment.update(enrollment_params)
    format.html { redirect_to @enrollment, notice: 'Enrollments was 
 successfully updated.' }
    format.json { render :show, status: :ok, location: @enrollment }
  else
    format.html { render :edit }
    format.json { render json: @enrollment.errors, status:      
:unprocessable_entity }
  end
end
end

# DELETE /enrollments/1
# DELETE /enrollments/1.json
def destroy
@enrollment.destroy
respond_to do |format|
  format.html { redirect_to enrollments_index_url, notice: 'Enrollments was 
successfully destroyed.' }
  format.json { head :no_content }
end
end

private
# Use callbacks to share common setup or constraints between actions.
def set_enrollment
  @enrollment = Enrollments.find(params[:id])
end

# Never trust parameters from the scary internet, only allow the white list 
through.
def enrollment_params
  params.require(:enrollment).permit(:student_id, :section_id)
end
end

Answer 1

该部分必须存在

该错误是因为您尝试使用 nil @enrollment保存section_id并引发该异常。问题出在您的表单上

<%= form.collection_select :section_number, Section.all, :id, 
:section_number, include_blank:false %>

应该是

<%= form.collection_select :section_id, Section.all, :id, 
:section_number, include_blank:false %>

初学者坚持Ruby on Rails项目“ ...必须存在”

1 个答案: