Rails：为什么我不能将新的模型实例保存到数据库？

Question

我的控制器的#create操作如下所示。我不知道为什么ruby/rails不接受参数赋值，因此我保存的对象有al"；nil"-属性

def create
@new_page = Page.new 
@new_page.slug = helpers.create_slug_from_title(params[:title])
# Yes, I should also save the rest of params and make
# params a strongparameter object

# how to handle errors on create ?
begin 
@new_page.save
rescue
end
end

如果有任何提示，我将不胜感激。

你的

von Spotz

附言：在控制台里，情况看起来并没有什么不同。

2.7.0 :038 > pn = Page.new
2.7.0 :039 > pn.slug = "index-page"
2.7.0 :040 > pn.slug
=> "index-page" 
2.7.0 :041 > pn
=> #<Page id: nil, text: nil, slug: nil, created_at: nil, updated_at: nil, title: nil, streams_id: nil> 
2.7.0 :042 > pn.save
(0.2ms)  begin transaction
Page Create (0.6ms)  INSERT INTO "pages" ("created_at", "updated_at") VALUES (?, ?)  [["created_at", "2021-05-07 17:01:15.111775"], ["updated_at", "2021-05-07 17:01:15.111775"]]
(31.5ms)  commit transaction
=> true 
2.7.0 :043 > Page.all
Page Load (0.2ms)  SELECT "pages".* FROM "pages" LIMIT ?  [["LIMIT", 11]]
=> #<ActiveRecord::Relation [#<Page id: 1, text: nil, slug: nil, created_at: "2021-05-07 15:40:59", updated_at: "2021-05-07 15:40:59", title: nil, streams_id: nil>, #<Page id: 2, text: nil, slug: nil, created_at: "2021-05-07 16:46:00", updated_at: "2021-05-07 16:46:00", title: nil, streams_id: nil>, #<Page id: 3, text: nil, slug: nil, created_at: "2021-05-07 17:01:15", updated_at: "2021-05-07 17:01:15", title: nil, streams_id: nil>]> 
2.7.0 :044 > 

PPS：带有创建操作和page_params的新控制器，由max 友好发布

class PagesController < ApplicationController

def home
end

def show
@page = Page.where(slug: params[:slug])
end

def new
@new_page = Page.new
end

def edit
@page = Page.where(slug: params[:slug])
# error if @page.nil?
end

# POST /pages
def create
@page = Page.new(page_params) do |page|
# smelly - should be handled inside the model not by the controller
page.slug = helpers.create_slug_from_title(page.title)
end

if @page.save
redirect_to @page, status: :created
else
render :new, status: :unprocessable_entity
end
end

private
def page_params
params.require(:page)
.permit(:slug, :title, :text)
end

end

Answer 1

class PagesController
# POST /pages
def create
@page = Page.new(page_params) do |page|
# smelly - should be handled inside the model not by the controller
page.slug = helpers.create_slug_from_title(page.title)
end
if @page.save
redirect_to @page, status: :created
else
render :new, status: :unprocessable_entity
end
end
private
def page_params
params.require(:page)
.permit(:foo, :bar, :title)
end
end

您通过重新呈现表单来处理经典web应用程序中的无效用户输入。begin ... rescue在此处不起作用，因为.save不会引发。save!确实如此，但它在这里的使用值得怀疑，因为例外情况应该用于例外情况——无效的用户输入是日常事件。

在表单上，您使用errors对象向用户显示验证错误：

<%= form_with(model: @page) do |f| %>
<% # @todo extract this into a partial %>
<% if f.object.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(f.object.errors.count, "error") %> prohibited this page from being saved:</h2>
<ul>
<% f.object.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>

<div class="field">
<%= f.label :title %>
<%= f.text_field :title %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>