我正在尝试在user和shipment模型之间建立关系。使用[devise] [1]生成users一切都很顺利，但现在我已经停止了。我收到此错误：
undefined method `first_name' for nil:NilClass
Shipment.rb
class Shipment < ActiveRecord::Base
belongs_to :user
end
User.rb
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
end
Shipments_Controller.rb
class ShipmentsController < ApplicationController
before_action :set_shipment, only: [:show, :edit, :update, :destroy]
# GET /shipments
# GET /shipments.json
def index
@shipments = Shipment.all
end
# GET /shipments/1
# GET /shipments/1.json
def show
end
# GET /shipments/new
def new
@shipment = Shipment.new
end
# GET /shipments/1/edit
def edit
end
# POST /shipments
# POST /shipments.json
def create
@shipment = Shipment.new(shipment_params)
respond_to do |format|
if @shipment.save
format.html { redirect_to @shipment, notice: 'Shipment was successfully created.' }
format.json { render :show, status: :created, location: @shipment }
else
format.html { render :new }
format.json { render json: @shipment.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /shipments/1
# PATCH/PUT /shipments/1.json
def update
respond_to do |format|
if @shipment.update(shipment_params)
format.html { redirect_to @shipment, notice: 'Shipment was successfully updated.' }
format.json { render :show, status: :ok, location: @shipment }
else
format.html { render :edit }
format.json { render json: @shipment.errors, status: :unprocessable_entity }
end
end
end
# DELETE /shipments/1
# DELETE /shipments/1.json
def destroy
@shipment.destroy
respond_to do |format|
format.html { redirect_to shipments_url, notice: 'Shipment was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_shipment
@shipment = Shipment.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def shipment_params
params.require(:shipment).permit(:user_id, :description, :from, :to, :date, :pay)
end
end
我的数据库迁移文件是：
devise_create_users.rb
class DeviseCreateUsers < ActiveRecord::Migration
def change
create_table(:users) do |t|
t.string :first_name
t.string :last_name
t.string :city_name
t.string :email, null: false, default: ""
t.string :encrypted_password, null: false, default: ""
## Recoverable
t.string :reset_password_token
t.datetime :reset_password_sent_at
## Rememberable
t.datetime :remember_created_at
## Trackable
t.integer :sign_in_count, default: 0, null: false
t.datetime :current_sign_in_at
t.datetime :last_sign_in_at
t.string :current_sign_in_ip
t.string :last_sign_in_ip
## Confirmable
# t.string :confirmation_token
# t.datetime :confirmed_at
# t.datetime :confirmation_sent_at
# t.string :unconfirmed_email # Only if using reconfirmable
## Lockable
# t.integer :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
# t.string :unlock_token # Only if unlock strategy is :email or :both
# t.datetime :locked_at
t.timestamps null: false
end
add_index :users, :email, unique: true
add_index :users, :reset_password_token, unique: true
# add_index :users, :confirmation_token, unique: true
# add_index :users, :unlock_token, unique: true
end
end
add_user_id_to_shipment.rb
class AddUserIdToShipments < ActiveRecord::Migration
def change
add_column :shipments, :user_id, :integer
add_index :shipments, :user_id
remove_column :shipments, :name
end
end
我的货件视图文件：
_form.html.erb
<%= simple_form_for(@shipment, html: {class: "form-horizontal"}) do |f| %>
<% if @shipment.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@shipment.errors.count, "error") %> prohibited this shipment from being saved:</h2>
<ul>
<% @shipment.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<%= f.input :user_id %>
<%= f.input :description %>
<div class="field">
<%= f.label :ship_from %><br>
<%= f.select :from, ['New York']%>
</div>
<div class="field">
<%= f.label :ship_to %><br>
<%= f.select :to, [ 'New york', 'Orlanda' ] %>
</div>
<%= f.input :date %>
<%= f.input :pay %>
<div class="form-actions">
<%= f.button :submit %>
</div>
<% end %>
Index.html.erb
<div class="page-header">
<h1>Listing Shipments</h1>
</div>
<%= link_to "Post a new Shipment", new_shipment_path, class: "btn btn-success" %>
<% @shipments.each do |shipment| %>
<div class="shipment">
<h3><strong><%= shipment.user.first_name %></strong></h3>
<h5><strong>DESCRIPTION: </strong><%= shipment.description %></h5>
<div class="meta">
<%= link_to time_ago_in_words(shipment.created_at) + " ago" %> |
<%= link_to "show", shipment %>
<span class="admin">
| <%= link_to "Edit", edit_shipment_path(shipment) %> |
<%= link_to "Delete", shipment, method: :delete, data: { confirm: "Are you sure?"} %>
</span>
</div>
</div>
<% end %>
Show.html.erb ＆lt;％= notice％＆gt;
<p>
<strong>Name:</strong>
<%= @shipment.user.first_name %>
</p>
<p>
<strong>Shipment Description:</strong>
<%= @shipment.description %>
</p>
<p>
<strong>Shipment From:</strong>
<%= @shipment.from %>
</p>
<p>
<strong>Ship To:</strong>
<%= @shipment.to %>
</p>
<p>
<strong>Shipment Date:</strong>
<%= @shipment.date %>
</p>
<p>
<strong>Pay:</strong>
<%= @shipment.pay %>
</p>
<%= link_to 'Edit', edit_shipment_path(@shipment) %> |
<%= link_to 'Back', shipments_path %>
我的命令行显示此日志：
Started GET "/" for ::1 at 2015-07-28 16:07:24 +0530
Processing by ShipmentsController#index as HTML
Shipment Load (0.0ms) SELECT "shipments".* FROM "shipments"
User Load (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT
1 [["id", 1]]
Rendered shipments/index.html.erb within layouts/application (0.0ms)
Completed 500 Internal Server Error in 16ms (ActiveRecord: 0.0ms)
ActionView::Template::Error (undefined method `first_name' for nil:NilClass):
6:
7: <% @shipments.each do |shipment| %>
8: <div class="shipment">
9: <h3><strong><%= shipment.user.first_name %></strong></h3>
10: <h5><strong>DESCRIPTION: </strong><%= shipment.description %></h5>
11: <div class="meta">
12: <%= link_to time_ago_in_words(shipment.created_at) + " ago" %> |
app/views/shipments/index.html.erb:9:in `block in _app_views_shipments_index_h
tml_erb__634505161_51269712'
app/views/shipments/index.html.erb:7:in `_app_views_shipments_index_html_erb__
634505161_51269712'
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/actionpack-4.2.3
/lib/action_dispatch/middleware/templates/rescues/_source.erb (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/actionpack-4.2.3
/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/actionpack-4.2.3
/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb
(0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/actionpack-4.2.3
/lib/action_dispatch/middleware/templates/rescues/template_error.html.erb within
rescues/layout (31.2ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/_markup.html.erb (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/_inner_console_markup.html.erb within layouts/inline
d_string (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/_prompt_box_markup.html.erb within layouts/inlined_s
tring (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/style.css.erb within layouts/inlined_string (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/console.js.erb within layouts/javascript (31.2ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/main.js.erb within layouts/javascript (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/error_page.js.erb within layouts/javascript (0.0ms)
Rendered C:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/web-console-2.2.
1/lib/web_console/templates/index.html.erb (78.0ms)
答案 0 :(得分：0)
看起来特定的shipment没有关联user。要快速解决问题，请尝试以下代码
<h3><strong><%= shipment.try(:user).try(:first_name) %></strong></h3>