Question

我想在3个模型之间创建一个多态关联 - 用户，帖子和评论。但是当我关联用户和帖子并添加表格＆＃39; user_id＆＃39;在视图＆post; / index＆＃39;浏览器显示错误

undefined method `name' for nil:NilClass

这是我的观点posts / index.html.haml

- @posts.each do |post|
  = post.title
  = post.body
  = post.user.name

这是我的帖子/ new.html.haml

= form_for @post do |f|
  = f.text_field :title, placeholder: "title"
  = f.text_field :body, placeholder: "text"
  = f.text_field :user_id, placeholder: "user"
  = f.submit "Send"

这是我的控制器posts_controller

class PostsController < ApplicationController

  def index
    @posts = Post.all
  end

  def new
    @post = Post.new
  end

  def create
    @post = Post.new(post_params)
    if @post.save
      redirect_to posts_path
    end
  end

  private

  def post_params
    params.require(:post).permit(:title, :body, :user_id)
  end
end

这是我的迁移create_posts.rb

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.string :title
      t.text :body
      t.references :user, index: true
      t.timestamps
    end
  end
end

这是我的模特帖子

class Post < ActiveRecord::Base
  belongs_to :user
end

UPD

2.1.5 :001 > Post.all   Post Load (0.6ms)  SELECT "posts".* FROM "posts"  => #<ActiveRecord::Relation [#<Post id: 1, title: "title", body: "body", user_id: nil, created_at: "2014-12-04 13:27:35", updated_at: "2014-12-04 13:27:35">, #<Post id: 2, title: "title", body: "body", user_id: nil, created_at: "2014-12-04 13:47:36", updated_at: "2014-12-04 13:47:36">, #<Post id: 3, title: "title", body: "body", user_id: 1, created_at: "2014-12-04 13:50:50", updated_at: "2014-12-04 13:50:50">, #<Post id: 4, title: "title", body: "body", user_id: 2, created_at: "2014-12-04 13:57:15", updated_at: "2014-12-04 13:57:15">]> 
2.1.5 :002 >

如何解决？

抱歉我的英文不好

Answer 1

每个人都填写了user_id吗？我猜这不是错误。简单的解决方法是在查找其名称之前测试是否存在用户。简单地说：

= post.user.name if post.user.present?

或，简短而甜蜜：

= post.user.try(:name)

为什么协会不工作。未定义的方法`name＆＃39;为零：NilClass

1 个答案: