rails tutorials: ActionPack

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ActionPack is Controller and View work together to let you interact with resources in the Model layer

REST(Representational State Transfer)

REST is all about resources, You should be to able to:

  1. List available resources
  2. Show a specific resource
  3. Destroy an existing resource
  4. Provide a way to create a new resource
  5. Create a new resource
  6. Provide a way to update an existing resource
  7. Update an existing resource

REST: A Simple Rails Convention

Rails Convention
Named Routes From

Index

Index action retrieves resources from Data layer. Then, implicitly invokes either HTML or JSON templates.

app/controllers/posts_controller.rb

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class PostsController < ApplicationController
  ...
  # GET /posts
  # GET /posts.json
  def index
    @posts = Post.all
  end
  ...
end

app/views/posts/show.html.erb

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

<h1>Listing Posts</h1>

<table>
  <thead>
    <tr>
      <th>Title</th>
      <th>Content</th>
      <th colspan="3"></th>
    </tr>
  </thead>

  <tbody>
    <% @posts.each do |post| %>
      <tr>
        <td><%= post.title %></td>
        <td><%= post.content %></td>
        <td><%= link_to 'Show', post %></td>
        <td><%= link_to 'Edit', edit_post_path(post) %></td>
        <td><%= link_to 'Destroy', post, method: :delete, data: { confirm: 'Are you sure?' } %></td>
      </tr>
    <% end %>
  </tbody>
</table>

<br>

<%= link_to 'New Post', new_post_path %>
  • post = post_path(post)
  • Destroy 和 Show 的 named route 都是 post, 因此 Destroy 需要指定 method: :delete

Show

  • Retrieve specific post based on id parameter passed in (as part of URL)
  • (Implicit) Look for show.html.erb template to render response

app/controllers/posts_controller.rb

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class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  ...

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

  ...

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

app/views/posts/show.html.erb

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

<p>
  <strong>Title:</strong>
  <%= @post.title %>
</p>

<p>
  <strong>Content:</strong>
  <%= @post.content %>
</p>

<%= link_to 'Edit', edit_post_path(@post) %> |
<%= link_to 'Back', posts_path %>

Delete

destroy action destroys a resource and then redirects the browser to another page

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class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  ...

  # DELETE /posts/1
  # DELETE /posts/1.json
  def destroy
    @post.destroy
    respond_to do |format|
      format.html { redirect_to posts_url, notice: 'Post was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

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

    ......
end

respond_to

  • Rails helper that specifies how to respond to a request based on a request format
  • Takes an optional block where the argument is the format
  • Block specifies how to handle each format:
    • format.format_name – matching template
    • format.format_name {do_something_other_than_just_displaying_the_ matching_template}

redirect_to

  • Instead of rendering a template – send a response to the browser: “Go here!”

New and Create

  1. New
  • Create a new empty post object
  • (Implicit) Look for new.html.erb
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class PostsController < ApplicationController

  # GET /posts/new
  def new
    @post = Post.new
  end

end
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<h1>New Post</h1>

<%= render 'form' %>

<%= link_to 'Back', posts_path %>
  1. Create
  • Create a new post object with parameters that were passed from the new form
  • Try to save the object to the database
  • If successful, redirect to show template
  • If unsuccessful, render new action (template - again)
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class PostsController < ApplicationController
  
  ...

  # POST /posts
  # POST /posts.json
  def create
    @post = Post.new(post_params)

    respond_to do |format|
      if @post.save
        flash[:success] = "Welcome to the Sample App!"
        format.html { redirect_to @post, notice: 'Post was successfully created.' }
        format.json { render :show, status: :created, location: @post }
      else
        format.html { render :new }
        format.json { render json: @post.errors, status: :unprocessable_entity }
      end
    end
  end


  private

    # Never trust parameters from the scary internet, only allow the white list through.
    def post_params
      params.require(:post).permit(:title, :content)
    end

    ...
end

Strong parameters

With strong parameters, Action Controller parameters are forbidden to be used in Active Model mass assigments until they have been whitelisted.

Flash

a hash where the data you put in persists for exactly ONE request AFTER the current request.

  • Two very common attributes are :notice (good) and :alert (bad)
  • These are so common in fact, that the redirect_to takes a :notice or :alert keys
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flash[:attribute] = value
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<% flash.each do |message_type, message| %>
<div class="alert alert-<%= message_type %>"><%= message %></div>
<% end %>

Edit and Update

  1. Edit
  • Retrieve a post object based on the id provided (as part of the URl)
  • (Implicit) Look for edit.html.erb
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class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  ...

  # GET /posts/1/edit
  def edit
  end

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

    ...
end
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<h1>Editing Post</h1>

<%= render 'form' %>

<%= link_to 'Show', @post %> |
<%= link_to 'Back', posts_path %>
  1. Update
  • Retrieve an existing post using id parameter
  • Update post object with (strong) parameters that were
    passed from the edit form
  • Try to (re)save the object to the database
  • If successful, redirect to show template
  • If unsuccessful, render edit action (template) again
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class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]

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


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

    # Never trust parameters from the scary internet, only allow the white list through.
    def post_params
      params.require(:post).permit(:title, :content)
    end

    ...
end

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