Activerecord RubyonRails：棘手的多对多关系不起作用

我正在我的应用程序中设计一个“列表”映射功能，用于代码转换。 因此，我的mappins_list对象指向源_list对象和目标_list对象，这两个对象都是实例值_list类。 该设计看起来很经典，但它的表现与预期不符：

 <td><%= link_to @mappings_list.source_list.name, @mappings_list.source_list%>

控制员在这里：

class MappingsListsController < ApplicationController
# Check for active session  
  before_action :signed_in_user

# Retrieve current current mapping
  before_action :set_mappings_list, only: [:show, :edit, :update, :destroy]

# Retrieve all lists of values
  before_action :set_values_lists

  # GET /mappings_list
  # GET /mappings_list.json
  def index
    @mappings_list = MappingsList.pgnd(current_playground).order("name")
  end

  # GET /mappings_list/1
  # GET /mappings_list/1.json
  def show
    ### Retrieved by Callback function
  end

  # GET /mappings_list/new
  def new
    @mappings_list = MappingsList.new
  end

  # GET /mappings_list/1/edit
  def edit
    ### Retrieved by Callback function
  end

  # POST /mappings_list
  # POST /mappings_list.json
  def create
    @mappings_list = MappingsList.new(mappings_list_params)
    @mappings_list.updated_by = current_user.login
    @mappings_list.created_by = current_user.login
    @mappings_list.playground_id = current_user.current_playground_id
    @mappings_list.owner_id = current_user.id

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

  # PATCH/PUT /mappings_list/1
  # PATCH/PUT /mappings_list/1.json
  def update
    ### Retrieved by Callback function
    @mappings_list.updated_by = current_user.login
    respond_to do |format|
      if @mappings_list.update(mappings_list_params)
        format.html { redirect_to @mappings_list, notice: 'List of mappings was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @mappings_list.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /mappings_list/1
  # DELETE /mappings_list/1.json
  def destroy
    ### Retrieved by Callback function
    @mappings_list.destroy
    respond_to do |format|
      format.html { redirect_to mappings_lists_url }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    # Check for active session
    def signed_in_user
      redirect_to signin_url, notice: "You must log in to access this page." unless signed_in?
    end

    def set_mappings_list
      @mappings_list = MappingsList.pgnd(current_playground).find(params[:id])
    end

    # retrieve the list of values lists
    def set_values_lists
      @lists_of_values = ValuesList.all
    end 

    # Never trust mappings from the scary internet, only allow the white list through.
    def mappings_list_params
      params.require(:mappings_list).permit(:name, :description, :source_list_id, :target_list_id)
    end
end

class-mappingslistscocontroller

双重引用值列表会使我的应用程序陷入麻烦吗

谢谢你的帮助

致以最良好的祝愿

---

Fred

在类映射列表中

类顺序

@order=@customer.orders

好的，我明白了

在索引视图中，在处理实例列表时，我不能引用一个实例变量，如@mappings\u list

该代码适用于以下情况：

        <td><%= link_to mappings_list.source_list.name, mappings_list.source_list%>

作为RoR的初学者，我希望我的解释是正确的

谢谢你的帮助

致以最良好的祝愿

---

Fred

共享正在渲染视图的控制器（出现错误的地方）。我刚刚注意到，在创建第一个示例时，在模型中保存之前调用的set_code函数工作正常。因此外键是有效的，这是一个很好的观点。不，实际上，每个源列表可以通过映射列表链接到不同的目标列表。源列表有许多映射列表，我使用FK声明从父源列表和目标列表中检索字段，这在其他模块中同样适用。

# == Schema Information
#
# Table name: mappings_lists
#
#  id             :integer          not null, primary key
#  playground_id  :integer
#  code           :string(255)
#  name           :string(255)
#  description    :text
#  created_by     :string(255)
#  updated_by     :string(255)
#  owner_id       :integer
#  source_list_id :integer
#  target_list_id :integer
#  created_at     :datetime
#  updated_at     :datetime
#


class MappingsList < ActiveRecord::Base

### scope
  scope :pgnd, ->(my_pgnd) { where "playground_id=?", my_pgnd }

### before filter
  before_create :set_code

### validation
    validates :name, presence: true, uniqueness: true, length: { maximum: 100 }
    validates :description, length: { maximum: 1000 }
    validates :created_by , presence: true
    validates :updated_by, presence: true
    validates :playground_id, presence: true
    belongs_to :playground
    validates :playground, presence: true                           # validates that the playground exists
    belongs_to :owner, :class_name => "User", :foreign_key => "owner_id"            # helps retrieving the owner name
    belongs_to :source_list, :class_name => "ValuesList", :foreign_key => "source_list_id"  # helps retrieving the source list name
    belongs_to :target_list, :class_name => "ValuesList", :foreign_key => "target_list_id"  # helps retrieving the target list name
    has_many :mappings

### private functions definitions
  private

  ### before filters
    def set_code 
      self.code = "#{source_list.code}_TO_#{target_list.code}"
    end 

end

  resources :values_lists do
    resources :values
    resources :mappings_lists
  end

class MappingsListsController < ApplicationController
# Check for active session  
  before_action :signed_in_user

# Retrieve current current mapping
  before_action :set_mappings_list, only: [:show, :edit, :update, :destroy]

# Retrieve all lists of values
  before_action :set_values_lists

  # GET /mappings_list
  # GET /mappings_list.json
  def index
    @mappings_list = MappingsList.pgnd(current_playground).order("name")
  end

  # GET /mappings_list/1
  # GET /mappings_list/1.json
  def show
    ### Retrieved by Callback function
  end

  # GET /mappings_list/new
  def new
    @mappings_list = MappingsList.new
  end

  # GET /mappings_list/1/edit
  def edit
    ### Retrieved by Callback function
  end

  # POST /mappings_list
  # POST /mappings_list.json
  def create
    @mappings_list = MappingsList.new(mappings_list_params)
    @mappings_list.updated_by = current_user.login
    @mappings_list.created_by = current_user.login
    @mappings_list.playground_id = current_user.current_playground_id
    @mappings_list.owner_id = current_user.id

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

  # PATCH/PUT /mappings_list/1
  # PATCH/PUT /mappings_list/1.json
  def update
    ### Retrieved by Callback function
    @mappings_list.updated_by = current_user.login
    respond_to do |format|
      if @mappings_list.update(mappings_list_params)
        format.html { redirect_to @mappings_list, notice: 'List of mappings was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @mappings_list.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /mappings_list/1
  # DELETE /mappings_list/1.json
  def destroy
    ### Retrieved by Callback function
    @mappings_list.destroy
    respond_to do |format|
      format.html { redirect_to mappings_lists_url }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    # Check for active session
    def signed_in_user
      redirect_to signin_url, notice: "You must log in to access this page." unless signed_in?
    end

    def set_mappings_list
      @mappings_list = MappingsList.pgnd(current_playground).find(params[:id])
    end

    # retrieve the list of values lists
    def set_values_lists
      @lists_of_values = ValuesList.all
    end 

    # Never trust mappings from the scary internet, only allow the white list through.
    def mappings_list_params
      params.require(:mappings_list).permit(:name, :description, :source_list_id, :target_list_id)
    end
end

        <td><%= link_to mappings_list.source_list.name, mappings_list.source_list%>