Rails 多个 select 放置额外的空白参数

Question

我正在尝试使用 collection_select 创建一个 HTML 多个 select，以便能够更新一个实体（Student），其中包含另一个实体（SubscriptionList）作为嵌套属性。这是由 HABTM ActiveRecord 的关系支持的。
我通过脚手架为学生创建了以下表格：

<div class="field">
  <%= f.label :first_name %><br>
  <%= f.text_field :first_name %>
</div>
<div class="field">
  <%= f.label :last_name %><br>
  <%= f.text_field :last_name %>
</div>
<div class="field">
  <%= f.label :file_number %><br>
  <%= f.text_field :file_number %>
</div>
<div class="field">
  <%= f.label :subscription_list %><br>
  <%= f.collection_select(:subscription_lists, SubscriptionList.all, :id, :name, {}, {:multiple => true}) %>
</div>

<div class="actions">
  <%= f.submit %>
</div>

并且它正确地绘制了倍数 select。
但是，如果我填写表格并尝试 PUT 实体，我会得到这个作为参数：

{"utf8"=>"✓", "_method"=>"patch", "authenticity_token"=>"vXYMRYI1UtX7WJRZM0OPIhHQSSEyNOPyUxkUvScdu45PTL7qVhvlJfQYNvaKG5rw+mvHAAAbf6ViTQ6tE4lV1Q==", "student"=>{"first_name"=>"玛丽安娜", "last_name"=>"González", "file_number"=>"12345678", "subscription_lists"=>["", "3"]} , "commit"=>"Update Student", "controller"=>"students", "action"=>"update", "id"=>"14" }

那么，我的学生是

"first_name"=>" Mariana", "last_name"=>"González", "file_number"=>"12345678", "subscription_lists"=>["", "3"]}

我觉得收到 ["", "3"] 作为值很奇怪。为什么我收到第一个 "" 值？

我也在这里发布我的控制器（为简洁起见，update 以外的操作已被删除）

class StudentsController < ApplicationController
  before_action :set_student, only: [:show, :edit, :update, :destroy, :enrollments]

  # PATCH/PUT /students/1
  # PATCH/PUT /students/1.json
  def update
    puts "\n\n\n\n\n\n\n\n\nThese are the params: #{params.inspect}"
    puts "\n\n\n\n\nThis is student_params object: #{student_params.inspect}\n\n\nand its class #{student_params.class}"
    #puts "\n\n\n\n\n\n\n\n\nWill look for SL with ID: #{params[:subscription_lists_id]}"
    all_ids = student_params.subscription_lists.collect {|sl| sl.id }
    @student.subscription_lists = SubscriptionList.find(all_ids)
    #@student.subscription_lists = SubscriptionList.where(id: all_ids)
    respond_to do |format|
      if @student.update(student_params)
        format.html { redirect_to @student, notice: 'Student was successfully updated.' }
        format.json { render :show, status: :ok, location: @student }
      else
        format.html { render :edit }
        format.json { render json: @student.errors, status: :unprocessable_entity }
      end
    end
  end

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

    # Never trust parameters from the scary internet, only allow the white list through.
    def student_params
      #params[:student]
      #params.require(:foo).permit(:bar, {:baz => [:x, :y]})
      #params.require(:student).permit(:first_name, :last_name, :file_number, :subscription_lists)

      params.require(:student).permit!    # No strong parameters...
    end
end

事实上，我宁愿接收带有 SubscriptionList 嵌套集合的 Student 而不是只接收一个 ID 数组，但我不确定这是否可能。

任何帮助将不胜感激。
最好的问候

Answer 1

关于您的问题已在 collection select always adding blank value 中得到解答。

如果您没有 select 任何东西，或者您 select 您的选项 select 默认情况下，您将获得 [""]。为避免这种情况，您必须在集合 select.

之前添加 hidden_field

<div class="field">
  <%= f.label :subscription_lists %><br>
  <%= f.hidden_field :subscription_lists %>
  <%= f.collection_select(:subscription_lists, SubscriptionList.all, :id, :name, {}, {:multiple => true}) %>
</div>

hidden_field 可以在您无所事事时为您提供帮助 select。选的时候怎么样？请试试这个。

  def update
    if student_params["subscription_lists"].any?
      student_params["subscription_lists"].reject!(&:empty?)
    end
    respond_to do |format|
      if @student.update(student_params)
        format.html { redirect_to @student, notice: 'Student was successfully updated.' }
        format.json { render :show, status: :ok, location: @student }
      else
        format.html { render :edit }
        format.json { render json: @student.errors, status: :unprocessable_entity }
      end
    end
  end

希望对你有所帮助。

Answer 2

这就是我最终所做的，主要是遵循 this tutorial。

对于控制器：

class StudentsController < ApplicationController
  before_action :set_student, only: [:show, :edit, :update, :destroy, :enrollments]

  # PATCH/PUT /students/1
  # PATCH/PUT /students/1.json
  def update
    puts "\n\n\n\n\n\n\n\n\nThese are the params: #{params.inspect}"
    puts "\n\n\n\n\nThis is student_params object: #{student_params.inspect}\n\n\nand its class #{student_params.class}"

    @subscription_lists = SubscriptionList.where(:id => params[:subscriptions])
    @student.subscription_lists.destroy_all   # disassociate the already added
    @student.subscription_lists << @subscription_lists

    respond_to do |format|
      if @student.update(student_params)
        format.html { redirect_to @student, notice: 'Student was successfully updated.' }
        format.json { render :show, status: :ok, location: @student }
      else
        format.html { render :edit }
        format.json { render json: @student.errors, status: :unprocessable_entity }
      end
    end
  end

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

    # Never trust parameters from the scary internet, only allow the white list through.
    def student_params
      params.require(:student).permit(:first_name, :last_name, :file_number, subscription_lists: [:id])
    end
end

以及表格：

  <div class="field">
    <%= f.label :subscription_list %><br>
    <%= select_tag "subscriptions", options_from_collection_for_select(SubscriptionList.all, 'id', 'name',@student.subscription_lists.map { |j| j.id }), :multiple => true %>
  </div>

希望有用

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