当我有两个多对多关联时，如何设置我的控制器和视图？

Question

我的目标是按类别整理上传的 post。这些类别显示在导航栏上，如果您单击其中一个类别的名称，您将看到分配有该类别的 post。上传 post 时，您也可以为其分配多个类别。所以，我认为这就像很多 post 可以有很多类别，很多类别可以有很多 post。

This is how I want my posts organized by categories

但是，我无法在 posts_controller.rb、posts/index.html.erb、posts/show.html.erb 和 _navigation.[=46] 中进行正确设置=]

post.rb

class Post < ActiveRecord::Base
  #This validates presence of title, and makes sure that the length is not more than 140 words
  validates :title, presence: true, length: {maximum: 140}
  #This validates presence of body
  validates :body, presence: true
    has_many :categorizations
    has_many :categories, :through => :categorizations 
end

category.rb

class Category < ApplicationRecord
    has_many :categorizations
    has_many :posts, :through => :categorizations
end

categorization.rb

class Categorization < ApplicationRecord
    belongs_to :post
    belongs_to :category
end

那么，这里是我混淆的控制器和视图：

posts_controller.rb

class PostsController < ApplicationController
  before_action :find_post, only: [:edit, :update, :show, :delete]
  before_action :authenticate_admin!, except: [:index, :show]
  # Index action to render all posts
  def index
    if params.has_key?(:category)
    @category = Category.find_by_name(params[:category])
    @posts = Post.where(category: @category)
    else
    @posts = Post.all
    end
  end

  # New action for creating post
  def new
    @post = Post.new
  end

  # Create action saves the post into database
  def create
    @post = Post.new(post_params)
    if @post.save
      flash[:notice] = "Successfully created post!"
      redirect_to post_path(@post)
    else
      flash[:alert] = "Error creating new post!"
      render :new
    end
  end

  # Edit action retrives the post and renders the edit page
  def edit
  end

  # Update action updates the post with the new information
  def update
    @post = Post.find(params[:id])
    if @post.update_attributes(post_params)
      flash[:notice] = "Successfully updated post!"
      redirect_to posts_path(@posts)
    else
      flash[:alert] = "Error updating post!"
      render :edit
    end
  end

  # The show action renders the individual post after retrieving the the id
  def show 
  end


  # The destroy action removes the post permanently from the database
  def destroy
    @post = Post.find(params[:id])
    if @post.present?
       @post.destroy
      flash[:notice] = "Successfully deleted post!"
      redirect_to posts_path
    else
      flash[:alert] = "Error updating post!"
    end
  end

  private

  def post_params
    params.require(:post).permit(:title, :body, category_ids: [])
  end

  def find_post
    @post = Post.find(params[:id])
  end
end

index.html.erb

<div class="container">
  <div class="col-sm-10 col-sm-offset-1 col-xs-12">
    <% @posts.each do |post| %>
    <div class="col-xs-12 text-center">
      <div class="text-center">
        <h2><%= post.title %></h2>
        <h6><%= post.created_at.strftime('%b %d, %Y') %></h6>
      </div>
      <div>
        <%= raw post.body.truncate(358) %>
      </div>
      <div class="text-center">
        <%= link_to "READ MORE", post_path(post) %>
      </div>
      <% if admin_signed_in? %>
        <%= link_to "Show", post_path(post), class: "btn btn-primary" %>
        <%= link_to "Edit", edit_post_path(post), class: "btn btn-default" %>
        <%= link_to "Delete", post_path(post), class: "btn btn-danger", data: {:confirm => "Are you sure?"}, method: :delete %>
      <% end %>
      <hr />
    </div>
    <% end %>
  </div>
</div>

显示.html.erb

<div class="col-sm-11 col-xs-12 blog-content">
  <h2 class="text-center"><%= @post.title %></h2>
  <h1 class="text-center"><%= @category.name %></h1>
  <h5 class="text-center"><%= @post.created_at.strftime('%b %d, %Y') %></h5>
  <div class="text-center"><%= raw @post.body %></div>
</div>

_navigation.html.erb（部分）

   <ul class="nav navbar-nav navbar-left">
    <% Category.all.each do |cat|  %>
    <li class="text-center"><%= link_to cat.name, posts_path(category: cat.name) %></li>
    <% end %>
   </ul>

以防万一，schema.rb

ActiveRecord::Schema.define(version: 2018_11_07_082317) do

  create_table "admins", force: :cascade do |t|
    t.string "email", default: "", null: false
    t.string "encrypted_password", default: "", null: false
    t.string "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "avatar"
    t.index ["email"], name: "index_admins_on_email", unique: true
    t.index ["reset_password_token"], name: "index_admins_on_reset_password_token", unique: true
  end

  create_table "categories", force: :cascade do |t|
    t.string "name"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "categories_posts", id: false, force: :cascade do |t|
    t.integer "category_id"
    t.integer "post_id"
  end

  create_table "categorizations", force: :cascade do |t|
    t.integer "post_id"
    t.integer "category_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "ckeditor_assets", force: :cascade do |t|
    t.string "data_file_name", null: false
    t.string "data_content_type"
    t.integer "data_file_size"
    t.string "type", limit: 30
    t.integer "width"
    t.integer "height"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["type"], name: "index_ckeditor_assets_on_type"
  end

  create_table "posts", force: :cascade do |t|
    t.string "title"
    t.text "body"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

end

Answer 1

在显示视图中您有

<h1 class="text-center"><%= @category.name %></h1>

但是您没有在 show 动作中定义 @category。如果要列出类别，应该是

<h1 class="text-center"><%= @post.categories.pluck(:name).join(', ') %></h1>

顺便说一句，看起来你在 schema.rb

中没有用 table categories_posts

更新：

关于索引操作 - 您应该更改 @posts 的查询，因为 post 没有类别列，但他有 categories 关联：

def index
  if params.has_key?(:category)
    # you can remove @category defining if you don't need it somewhere in view
    @category = Category.find_by_name(params[:category])
    @posts = Post.joins(:categories).where(categories: { name: params[:category] } )
  else
    @posts = Post.all
  end
end

注意，查询最好用id，不要用name，用id搜索更快。您需要将导航栏中的 link 更改为 link_to cat.name, posts_path(category: cat.id)，并在查询中将 name 替换为 id。最好将整个查询移动到 Post 模型中的命名范围。

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