Ruby学习笔记5: 动态web app的建立 （2）

上一节里，我们搭建了一个数据库的结构，并用index验证了request-response cycle，如下图：

1. Add show method into Controller

这一节，我们要继续丰富我们的controller:
While index gave all categories, show allows us to access one category. This this is helpful when we want to show just one Category at a time in our Etsy app.

The show method works like this. we write:

[ruby] view plaincopy

1. def show  
2.   @category = Category.find(params[:id])    #it's a hash that we use to find an object by its unique id
   
3. end 
   

The show method finds a single category of a given id and stores it in @category. Look a little closer at params[:id]. Seem familiar?
It's a hash that we use to find an object by its unique id. We can find the exact object we want.
我们知道，【在main Controller里的每个action都需要一个route & view】
这里我们在controller里加入了show method，Rails自动update了the route and the view for us.

提醒：在route.rb文件中，我们已有的语句：resources :categories已经takes care of our route for show. Rails 还创建了show.html.erb在我们的Views中!
Rails did this for show, just like it did for the index method.

Rails generates these when we enter methods in your rails generate controller command[rails generate controller Categories index show new edit delete], other we need do it manually.

此时我们的routes.rb还是老样子：

Rails.application.routes.draw do
  get '/' => 'pages#home'
resources :categories
get 'categories/:id/delete' => 'categories#delete', :as => :categories_delete
end

<%= render 'shared/topnav' %>
<p>
  <strong>Name:</strong>
  <%= @category.name %>
</p>

<p>
  <strong>Thumburl:</strong>
  <%= image_tag @category.thumburl %>
</p>
<%= link_to 'Edit', edit_category_path(@category) %> |
<%= link_to 'Back', categories_path %>
<%= render 'shared/footer' %>

2. Forms in html - 表单请求

 <%= form_for (@category) do |f| %>  <!--for the person at hand, we'll pass the following information to our form.-->
   <div class="field">  
   <%= f.label :name %><br>   <!--Heading for name, labels in Rails, allow us to label our field -!--冒号后面不能有空格--->
   <%= f.text_field :name %>  <!--The field where we put our stuff, text_field is for text, -->
   </div>
<div class="field">
<%= f.label :thumburl %><br>
<%= f.url_field :thumburl %>  <!–rails we can use url_field for things like urls–>
</div>
<div class='actions'>
<%= f.submit %> <!–the button to submit the form.–>
</div>
<% end %>

===================================

好了，我们要接着写 增加 的Controller methods 了。

3. Add 'new' and 'create' method into Controller

def new
    @category = Category.new  #creating a whole new instance of Category, and storing it in @category
end

The create method looks like this:

def create
 @category = Category.new(category_params)  #save that information as our new data through our strong params method
 if @category.save
  redirect_to(:action => 'index') #If it saves, we redirect to the index page
 else
  render('new') #otherwise the new page will render again.
 end
end

class CategoriesController < ApplicationController
  def index
    @categories = Category.all
  end
def show
@category = Category.find(params[:id])
end
def new
@category = Category.new
end
def create
@category = Category.new(category_params)  # I do not udrstand the .new and the ()
if @category.save
redirect_to(:action => 'index')
else
render('new')
end
end
def edit
end
def delete
end
private
def category_params
params.require(:category).permit(:name, :thumburl)
end
end

<%= render 'form' %>

<%= render 'shared/topnav' %>
<h1>New Category</h1>
<!– Render form here –>
<%= render 'form' %>
<%= link_to 'Back', categories_path %>
<%= render 'shared/footer' %>

然后我们就得到了这个：

===================================

好了，我们要接着写 改 的Controller methods 了。

4. Add 'edit' and 'update' method into Controller

The edit method looks like this:

def edit
  @category = Category.find(params[:id])
end

edit method 就是根据id找到category并把它存入@category中。跟show method是一模一样的。这还不够，我们还要一个update method来存它。

def update
  @category = Category.find(params[:id])  #find a category by its id
  if @category.update_attributes(category_params)
    redirect_to(:action => 'show', :id => @category.id)
  else
    render('index')
  end
end

class CategoriesController < ApplicationController
  def index
    @categories = Category.all
  end
def show
@category = Category.find(params[:id])
end
def new
@category = Category.new
end
def create
@category = Category.new(category_params)
if @category.save
redirect_to(:action => 'index')
else
render('new')
end
end
def edit
@category = Category.find(params[:id]) #finds a single category of a given id and stores it in @category
end
def update
@category = Category.find(params[:id]) #finds a person by its id and stores it in person
if @category.update_attributes(category_params)#check if the attributes are updated in our model
redirect_to(:action => 'show', :id => @category.id)#go to show page for that object
else
render('index') #render our index again
end
end
def delete
end
private

def category_params
params.require(:category).permit(:name, :thumburl)
end
end

接下来是修改view: app/views/categories/edit.html.erb
We just need an edit page and the update page will process the information.
Here, our form_for comes in handy again. We go to our edit page and write: <%= render 'form' %>
That's it. We're good!

<%= render 'shared/topnav' %>
<h1>Edit Category</h1>
<!– Render form here –>
<%= render 'form' %>
<%= link_to 'Back', categories_path %>
<%= render 'shared/footer' %>

===================================

好了，我们要接着写 删 的Controller methods 了。

5. Add 'delete' and 'destroy' method into Controller

we could write a delete method like this:

def delete
  @category = Category.find(params[:id])
end

它看起来有点像show & edit，The destroy method looks like this:

def destroy
  Category.find(params[:id]).destroy 
  redirect_to(:action => 'index')
end

Here we find a category we want to permanently delete. Once we delete it, we get redirected to the index page.

修改view： app/views/categories/delete.html.erb 成：

<p>
  <strong>Name:</strong>
  <%= @category.name %>
</p>
<p>
<strong>Thumburl:</strong>
<%= image_tag @category.thumburl %>
</p>
<%= link_to "Delete", categories_delete_path(:id => @category.id) %> |
<%= link_to 'Edit', edit_category_path(@category) %> |
<%= link_to 'Back', categories_path %>
<p>1</p>
<p>2</p>
<p>3</p>

Congratulations! You created the Categories page of the Etsy app. We did this by creating the Model, Controller, and Views for Categories.

总结一下：

We first generated the Category Model using a terminal command. We added columns to our Categories Migration table and migrated and seeded our database.

We then generated a Categories Controller with the index, show, new, edit, and delete methods. This gave us a route and View for those methods.

We created Controller methods for eight of our CRUD actions, and Views for index, show, new, edit, and delete.

• 首先在terminal command里建立了Model， 我们在注入表里加入了columns到Categories,并且，我们Seeded our database.
  
• 然后我们建立了categories controller with the index, show, new, edit, and delete methods. 这让我们有了routes 和 view for those methods.
• 我们8个CRUD actions 所需的methods都建立在了controller里，index, show, edit ,and delete所需的Views也建立了。