Question

当我想创建一本新书时，我需要将它附加到类别。但是当我试图保存一本新书时，我收到了错误：＆＃34;找不到带有＆lt;的类别。 id＆＃34; =＆＃34;。＆GT;我不知道为什么，但除了我已经附上的那些之外还有一个id附加。这个id是空的（＆＃34;＆＃34;）。它看起来像这样（＆＃34;书＆＃34; =＆gt; {＆＃34;名称＆＃34; =＆gt;＆＃34; 12＆＃34;，＆＃34; category_ids＆＃34; =＆gt; [＆＃34;＆＃34;，＆＃34; 2＆＃34;，＆＃34; 7＆＃34;]，......）。请帮帮我。我的bookcontroler：

def new 
 @book = Book.new(book_params)
end

def create 
 @book = Book.new(book_params)
 @category = Category.find(id: params[:ids])
 BookCategory.create!(book: @book, category: @category)
 @book.save
end

private

def book_params
 params.require(:book).permit(:name, :author, :image, :description)
end

我的表格：

    <%= form_for (@book) do |f| %>
      <%= f.collection_select :category_ids, Category.order(:name), :id, :name, {},{ multiple: :true } %><br>
    <% end %>

我的错误：enter image description here

Answer 1

如果您已正确设置关联：

class Book < ApplicationRecord
  has_many :book_categories
  has_many :categories, through: :book_categories
end

class Category < ApplicationRecord
  has_many :book_categories
  has_many :books, through: :book_categories
end

class BookCategory < ApplicationRecord
  belongs_to :book
  belongs_to :category
end

对于每个has_many关联，ActiveRecord会创建一个_ids setter和getter：

@book = Book.find(1)
@book.category_ids 
# => [1, 2, 3]
@book.category_ids = [2,4]  # will add 4 and remove 1 and 3.

因此您无需手动设置关联，只需传递category_ids参数：

def new 
 @book = Book.new # don't assign params in the new method!
end

def create 
  @book = Book.new(book_params)
  if @book.save
    redirect_to @book
  else
    render :new
  end
end

private

def book_params
  # category_ids: [] allows an array of scalar values
  params.require(:book)
        .permit(:name, :author, :image, :description, category_ids: [])
end

由于您使用的.find数组参数可能为零或为空，因此您的代码无效。

collection_select的options参数也是可选的：

<%= form_for (@book) do |f| %>
  <%= f.collection_select :category_ids, Category.order(:name), :id, :name, { multiple: :true } %><br>
<% end %>

多选：附加一个额外的空ID

1 个答案: