将Rails find_or_create_by与表单对象一起使用

我正在创建一个Rails库应用，其中有一种类型的has_many书和belongs_to一种类型的书。我需要使用表单对象，因为我的数据模型最终将具有多个多对多的关系，并且因为我想学习如何使用表单对象。我已经基于Rails Cast＃416表单对象创建了表单对象。我的表单，表单对象，模型和控制器似乎都可以正常工作。创建了新书并将它们与流派相关联，但是它们都是流派“流派”。我正在使用find_or_create_by。我认为问题出在book_form.rb哪里@genre ||= Genre.find_by(name: :name)，实际上没有从表单中传递流派信息。我的相关代码如下：

样板书.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，我可以从服务器上获得这本书：

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，书体裁正在参数中传递，但是我在书本形式中访问的方式错误。如果我将其注释掉binding.pry，则该表格会创建一本类型为“名称”的新书，而不是像我希望的那样类型为“神秘”的书。

当我@genre在使用binding.pry的同时输入rails时，我得到

[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 ] [：name]）31：结束