ruby-on-rails - Rails 未定义的方法 - NoMethodError

Question

我在模糊地关注 http://guides.rubyonrails.org/getting_started.html ，第 6 部分。

使用 Rails v 4.1.8SQLite 数据库

添加第二个模型后出现此错误:

NoMethodError in Pages#show

Showing M:/ICT/Rails/Salacity/app/views/pages/show.html.erb where line

24 raised:

undefined method `links' for #

Extracted source (around line #24)

Links

<% @page.links.each do |link| %>

ID: <%= link.child__id %>

Rails.root: M:/ICT/Rails/Salacity Application Trace | Framework Trace | Full Trace

app/views/pages/show.html.erb:24:in `_app_views_pages_show_html_erb___283878207_51684456'

这是 app/views/pages/show.html.erb

<p id="notice"><%= notice %></p>

<p>
  <strong>Page:</strong>
  <%= @page.page_id %>
</p>

<p>
    <strong>Body:</strong>
    <%= @page.body %>
</p>

<p>
    <strong>Branch:</strong>
    <%= @page.branch_id %>
</p>

<p>
    <strong>Location:</strong>
    <%= @page.location_id %>
</p>

<h2>Links</h2>
<% @page.links.each do |link| %>
    <p>
        <strong>ID:</strong>
        <%= link.child__id %>
    </p>

    <p>
        <strong>Body:</strong>
        <%= link.body %>
    </p>
<% end %>

<h2>Add a link:</h2>
<%= form_for([@page, @page.links.build]) do |f| %>
    <p>
        <%= f.label :page_id %><br>
        <%= f.text_field :page_id %>
    </p>
    <p>
        <%= f.label :child_id %><br>
        <%= f.text_area :child_id %>
    </p>
    <p>
        <%= f.label :order %><br>
        <%= f.number_field :order %>
    </p>
    <p>
        <%= f.label :body %><br>
        <%= f.text_area :body %>
    </p>
    <p>
        <%= f.submit %>
    </p>
<% end %>


<%= link_to 'Edit', edit_page_path(@page) %> |
<%= link_to 'Back', pages_path %>

页面 Controller

class PagesController < ApplicationController
  before_action :set_page, only: [:show, :edit, :update, :destroy]

  # GET /pages
  # GET /pages.json
  def index
    @pages = Page.all
  end

  # GET /pages/1
  # GET /pages/1.json
  def show
    @page = Page.find(show_params)
  end

  # GET /pages/new
  def new
    @page = Page.new
  end

  # GET /pages/1/edit
  def edit
    @page = Page.find(params[:id])
  end

  # POST /pages
  # POST /pages.json
  def create
    @page = Page.new(page_params)

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

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

  # DELETE /pages/1
  # DELETE /pages/1.json
  def destroy
    @page = Page.find(params[:id])
    @page.destroy

    respond_to do |format|
     format.html { redirect_to pages_url, notice: 'Page was successfully destroyed.' }
     format.json { head :no_content }
    end
  end

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

    # Never trust parameters from the scary internet, only allow the white list through.
    def page_params
      params.require(:page).permit(:page_id, :body, :branch_id, :location_id)
    end

    def show_params
      params.require(:id)
    end
end

链接 Controller

class LinksController < ApplicationController
  before_action :set_link, only: [:show, :edit, :update, :destroy]

  # GET /links
  # GET /links.json
  def index
    @links = Link.all
  end

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

  # GET /links/new
  def new
    @link = Link.new
  end

  # GET /links/1/edit
  def edit
  end

  # POST /links
  # POST /links.json
=begin
  def create
    @link = Link.new(link_params)

    respond_to do |format|
      if @link.save
        format.html { redirect_to @link, notice: 'Link was successfully created.' }
        format.json { render :show, status: :created, location: @link }
      else
        format.html { render :new }
        format.json { render json: @link.errors, status: :unprocessable_entity }
      end
    end
  end
=end
  def create
    @page = Page.find(params[:page_id])
    @link = @page.links.create(link_params)
    redirect_to page_path(@page)
  end


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

  # DELETE /links/1
  # DELETE /links/1.json
  def destroy
    @link.destroy
    respond_to do |format|
      format.html { redirect_to links_url, notice: 'Link was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

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

    # Never trust parameters from the scary internet, only allow the white list through.
    def link_params
      params.require(:link).permit(:page_id, :child_id, :order, :body)
    end
end

Class Page has_many :links 和 Class Link belongs_to :page迁移都已完成数据库中存在链接表不知道还有什么地方可以看!

提前致谢

编辑:我也遇到这个错误

ActiveRecord::StatementInvalid in Pages#show

Showing M:/ICT/Rails/Salacity/app/views/pages/show.html.erb where line

24 raised:

SQLite3::SQLException: no such column: links.page_id: SELECT "links".* FROM "links" WHERE "links"."page_id" = ?

Extracted source (around line #24):

Links

<% @page.links.each do |link| %>

ID: <%= link.child__id %>

Rails.root: M:/ICT/Rails/Salacity Application Trace | Framework Trace | Full Trace

app/views/pages/show.html.erb:24:in `_app_views_pages_show_html_erb___283878207_50250936'

db/migrate/create_links.rb

class CreateLinks < ActiveRecord::Migration
  def change
    create_table :links do |t|
      t.text :page_id
      t.text :child_id
      t.integer :order
      t.text :body
      t.references :page, foreign_key: true, index: true

      t.timestamps
    end
  end
end

和schema.rb

# encoding: UTF-8
# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# Note that this schema.rb definition is the authoritative source for your
# database schema. If you need to create the application database on another
# system, you should be using db:schema:load, not running all the migrations
# from scratch. The latter is a flawed and unsustainable approach (the more migrations
# you'll amass, the slower it'll run and the greater likelihood for issues).
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 20150707195306) do

# Could not dump table "branches" because of following NoMethodError
#   undefined method `[]' for nil:NilClass

# Could not dump table "keywords" because of following NoMethodError
#   undefined method `[]' for nil:NilClass

# Could not dump table "links" because of following NoMethodError
#   undefined method `[]' for nil:NilClass

# Could not dump table "locations" because of following NoMethodError
#   undefined method `[]' for nil:NilClass

# Could not dump table "pages" because of following NoMethodError
#   undefined method `[]' for nil:NilClass

end

Answer 1

像这样更改您的迁移文件

db/migrate/timestamp_create_links.rb

class CreateLinks < ActiveRecord::Migration
  def change
    create_table :links do |t|
      t.integer :child_id
      t.integer :order
      t.text :body
      t.references :page, index: true

      t.timestamps
    end
  end
end