NilClass:Class 的 Rails 未定义方法“model_name" [英] Rails undefined method `model_name' for NilClass:Class

问题描述

我有一个表单，我想出现在每个页面的顶部，所以我将它包含在/app/views/layouts/application.html.erb 文件中，但出现错误 undefined methodmodel_name' for NilClass:Class` 尝试加载页面时.

这是 application.html.erb 中的表单片段

 <%= form_for @user do |f|％＞<h3>添加新联系人</h3><%= f.text_field :first_name %><br/><%= f.text_field :last_name %><%= f.text_field :email %><小时/><%= f.submit "添加联系人" %><%结束%>

这是我的/app/controllers/user_controller.rb

class UserController <应用控制器定义索引结尾定义新@user = User.new结尾结尾

我认为我遇到了这个错误，因为表单在 application.html.erb 文件中，我需要以某种方式指定路径，但我又一次对 rails 很陌生.

如果您需要发布任何其他内容，请告诉我.

编辑按照 Ola 的建议，在我的 app/views/layouts/application.html.erb 文件中，我有这样的内容:

<%=yield :add_user %>

在我的 app/views/users/new.html.erb 文件中我有这个

<% content_for :add_user do %><%= form_for @user do |f|％＞<h3>添加新联系人</h3>名字
<%= f.text_field :first_name %><br/>姓氏<br/><%= f.text_field :last_name %><br/>电子邮件<br/><%= f.text_field :email %><小时/><%= f.submit "添加联系人" %><%结束%><%结束%>

表单未呈现，因为我的 url 是 http://localhost:3000/admin/index，所以它在 app/views/中寻找 add_user content_foradmin/index.html.erb

解决方案

如果表单包含在多个操作(页面)中，您需要将 @user 设置为 something 或 form_for 指令将失败(它没有任何内容可以为 for 创建表单).

更好的方法(和 Rails 默认)是为每个动作设置单独的视图，每个视图只包含该动作所需的元素，并加载到您的 application.html.erb 布局中<%= 产量 %>.所以你会有一个 app/views/users/new.html.erb 视图，其中包含表单.您从不很少需要在Rails 中定义任何加载路径，它们都来自模型、控制器和动作名称——或者来自您的routes.rb.这是约定优于配置 范式的核心部分，该范式运行在 Rails 中如此深入.

如果您确实需要有一个表单来在每个页面上创建一个新对象(例如通常用于 UserSessions)，您可以重写您的 form_for 使其不依赖于存在的对象:

form_for(User.new)

或者如果你需要强制它发布到 create 方法

form_for(User.new, :url => { :action => "create" })

您可以在 Ruby On Rails API 文档.

I have a form that i want to appear at the top of every page so i've included it in the /app/views/layouts/application.html.erb file and i get the error undefined methodmodel_name' for NilClass:Class` when trying to load the page.

Here's the form snippet in application.html.erb

 <%= form_for @user do |f| %>
    <h3>Add new contact</h3>
    <%= f.text_field :first_name %><br />
    <%= f.text_field :last_name %>
    <%= f.text_field :email %>
    <hr />
    <%= f.submit "Add Contact" %>
<% end %>

Here's my /app/controllers/user_controller.rb

class UserController < ApplicationController

    def index

    end

    def new
        @user = User.new
    end

end

I'm thinking that i'm hitting this error because since the form is in the application.html.erb file, i need to somehow specify the path, but then again i'm very new to rails.

Let me know if you need anything else posted.

EDIT Following Ola's suggestion, In my app/views/layouts/application.html.erb file I have something like this:

<div>
<%= yield :add_user %>
</div>

and in my app/views/users/new.html.erb file I have this

<% content_for :add_user do %>
    <%= form_for @user do |f| %>
        <h3>Add new contact</h3>
        First Name<br />
        <%= f.text_field :first_name %><br />
        Last Name<br />
        <%= f.text_field :last_name %><br />
        Email<br />
        <%= f.text_field :email %>
        <hr />
        <%= f.submit "Add Contact" %>
    <% end %>
<% end %>

The form is not rendered because my url is http://localhost:3000/admin/index and so it's looking for the add_user content_for in app/views/admin/index.html.erb

解决方案

If the form is included for multiple actions (pages) you need to set @user to something or the form_for directive will fail (it won't have anything to create a form for).

A much better approach (and the Rails default) is to have separate views for each action, each including only the elements required by that action, and loaded into your application.html.erb layout with <%= yield %>. So you would have a app/views/users/new.html.erb view which has the form in it. You never very rarely need to define any load paths in Rails, they are all derived from the model, controller and action names - or from your routes.rb. This is a core part of the convention over configuration paradigm which runs so deep in Rails.

Edit: If you do need to have a form for creating a new object on every page (often used for UserSessions for example), you can rewrite your form_for so that it doesn't depend on an object being present:

form_for(User.new)

or if you need to force it to post to the create method

form_for(User.new, :url => { :action => "create" }) 

You can read more about resource driven form_for in the Ruby On Rails API docs.

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