我的目的是按类别组织上传的帖子。这些类别显示在导航栏上，如果您单击类别名称之一，则将看到分配给该类别的帖子。上传帖子时，您也可以为其分配多个类别。因此，我认为这就像很多帖子可以有很多类别，很多类别可以有很多帖子。
This is how I want my posts organized by categories
但是，我无法在我的posts_controller.rb，posts / index.html.erb，posts / show.html.erb和_navigation.html.erb中正确设置
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
然后，这些是我困惑的控制器和视图：
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>
show.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（一部分）
<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
答案 0 :(得分：0)
在显示视图中，您拥有
<h1 class="text-center"><%= @category.name %></h1>
但是您没有在表演动作中定义@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，看来您在schema.rb中有无用的表categories_posts
更新：
关于索引操作-您应该更改@posts的查询，因为该帖子没有类别列，但是他具有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
请注意，最好将id用于查询，而不要使用name，按id搜索会更快。您需要将其导航栏中的链接更改为link_to cat.name, posts_path(category: cat.id)，并在查询中将name替换为id。最好将整个查询移到Post模型中的命名范围。