使用Rails find_or_create_by和表单对象

Question

我正在创建一个Rails库应用程序,其中有一个类型的has_many书籍和一本书belongs_to类型.我需要使用表单对象,因为我的数据模型最终会有多个多对多关系,因为我想学习如何使用表单对象.我已经将我的表单对象基于Rails Cast#416表单对象.我的表单,表单对象,模型和控制器似乎都可以工作.新书被创建并且它们与流派相关联,但它们都是流派"流派".我在用find_or_create_by.我认为问题出在book_form.rb那里@genre ||= Genre.find_by(name: :name)实际上没有传递从形式体裁信息.我的相关代码如下:

模型book.rb

class Book < ActiveRecord::Base
  belongs_to :genre
  before_save :convert_isbn
.
.
.
end

型号genre.rb

class Genre < ActiveRecord::Base
  has_many :books, dependent: :destroy
  validates_associated :books
end

book_form.rb

class BookForm
  include ActiveModel::Model

  def self.model_name
    ActiveModel::Name.new(self, nil, "Book")
  end
.
.
.
  validates :name, presence: true

  delegate :name, to: :genre
  delegate :title, :year, :pages, :isbn, :summary, :volume_a, :volume_b, to: :book

  def genre
    @genre ||= Genre.find_by(name: :name)
  end

  def book
    @book ||= genre.books.build
  end

  def submit(params)
    genre.attributes = params.slice(:name).permit(:name)
    book.attributes = params.slice(:title, :year, :pages, :isbn, :summary, :volume_a,:volume_b).permit(:title, :year, :pages, :isbn, :summary, :volume_a,:volume_b)
    if valid?
      genre.save!
      book.save!
      true
    else
      false
    end
  end
end

books_controller.rb

class BooksController < ApplicationController
  before_action :admin_user, only: [:new, :edit, :destroy]

  def new
    @book_form = BookForm.new
    @genres = Genre.all
  end

  def create
    @book_form = BookForm.new
    @genres = Genre.all
    if @book_form.submit(params[:book])
      flash[:success] = "You've added a new book to the library!"
      redirect_to @book_form
    else
      render 'new'
    end
  end

查看new.html.erb

<%= form_for @book_form do |f| %>
  <%=render 'shared/error_messages', object: f.object %>

  <%= f.label :title %>
  <%= f.text_field :title, class: 'form-control' %>
  .
  .
  .
  <%= f.label :genre %><br>

  <%= collection_select(:genre, :name, Genre.all, :name, :name) %>
  <br>
  <br>
  <%= f.submit "Add book to library", class: "btn btn-primary" %>
<% end %>

使用Pry gem,我在创建一本书时从服务器获取:

Started POST "/books" for ::1 at 2016-02-22 14:19:20 -0700
Processing by BooksController#create as HTML
  Parameters: {"utf8"=>"?",     "authenticity_token"=>"bPusgyl9n+p07eQsEAe9CpSsithtkg33HMifj8KTsidv3GDLuhjibOC7d2mm5boC4w7ZUne64R4n4OMQotDE4g==",
               "book"=>{"title"=>"test",
               "year"=>"2016",
               "pages"=>"222",
               "isbn"=>"9780-xx-xx-xx",
               "summary"=>"fake summary",
               "volume_a"=>"1",
               "volume_b"=>"2"},
               "genre"=>{"name"=>"Mystery"},
               "commit"=>"Add book to library"}

From: /home/nathaniel/rails_apps/allredlib/app/forms/book_form.rb @ line 38 BookForm#submit:

    37: def submit(params)
 => 38:   binding.pry
    39:   genre.attributes = params.slice(:name).permit(:name)
    40:   book.attributes = params.slice(:title, :year, :pages, :isbn, :summary, :volume_a,:volume_b).permit(:title, :year, :pages, :isbn, :summary, :volume_a,:volume_b)
    41:   if valid?
    42:     genre.save!
    43:     book.save!
    44:     true
    45:   else
    46:     false
    47:   end
    48: end

因此,书籍类型在参数中得到了传递,但我在书本表格中以错误的方式访问它.如果我发表评论binding.pry,该表格会创建一个新书,其中包括流派"名称",而不是像我希望的那样流派"神秘".

当我@genre使用binding.pry 键入rails时,我得到了

[1] pry(#<BookForm>)> @genre
=> #<Genre:0x007f19554e1220
 id: 20,
 name: "name",
 book_id: nil,
 created_at: Thu, 25 Feb 2016 20:28:45 UTC +00:00,
 updated_at: Thu, 25 Feb 2016 20:28:45 UTC +00:00>

最新的binding.pry结果27:def genre => 28:binding.pry 29:@genre || = Genre.find_or_initialize_by(name :: name)30:#@ genre || = Genre.find_or_initialize_by(name:params [:genre ] [:姓名])31:结束

Answer 1

如果您要通过名称查找流派，那么您需要在方法的选项哈希中传入名称属性。

def genre
  @genre ||= Genre.find_or_create_by(name: :name)
end

更新

改变

genre.attributes = params.slice(:name).permit(:name)

到

genre.attributes = { :name => params[:genre][:name] }

还要在genre.save之前和之后扔bounding.pry！看看你输入时会得到什么，@genre 因为你的类型方法应该创建了你刚刚发送参数的实例变量genre.attributes该变量接受哈希值。

我会在书籍参数上考虑相同的问题，但如果切片工作得很好。

另外，由于您在表单视图中调用Genre.all，因此您可能不需要在控制器操作中执行此操作，但如果这样做，请考虑使用@genres表单视图中的对象collection_select，因为您将发出所有请求两次在模型上。

@genres = Genre.all