Rails多重选择添加额外的空白参数

Question

我试图使用collection_select创建一个HTML多重选择，以便能够更新一个实体(Student)，它具有另一个实体(SubscriptionList)的集合作为嵌套属性。这是由HABTM ActiveRecord的关系备份的。
我已经通过脚手架为学生创建了以下表单:

<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>

，它正确地绘制了多重选择。
但是，如果我填写表单并尝试PUT实体，我将得到以下参数:

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

那么，我的Student是

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

我发现接收["", "3"]作为值是非常奇怪的。为什么我收到这个第一个""值?

我也在这里张贴我的控制器(动作，update已被删除为简洁)

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 "nnnnnnnnnThese are the params: #{params.inspect}"
    puts "nnnnnThis is student_params object: #{student_params.inspect}nnnand its class #{student_params.class}"
    #puts "nnnnnnnnnWill 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Student与SubscriptionList的嵌套集合，而不是仅仅接收一个id数组，但我不确定这是否可能。

任何帮助都将非常感激。
最好的祝福

Answer 1

关于您的问题已在collection中得到回答，select总是添加空白值。

你将得到[""]当你没有选择任何东西或你选择你的选项选择作为默认值。为了避免这种情况，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在没有选择时可以帮助您。当你选择它的时候呢?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

Answer 2

这就是我最终所做的，主要是遵循本教程。

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 "nnnnnnnnnThese are the params: #{params.inspect}"
    puts "nnnnnThis is student_params object: #{student_params.inspect}nnnand 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

和形式:

  <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>

希望对大家有用