获取ActiveModel::MissingAttributeError:同时使用ROR插入数据

Question

在使用ROR通过rails控制台将数据插入数据库时，我得到了以下错误。

错误：

irb(main):004:0> book.comments << comment
   (1.0ms)  begin transaction
   (0.0ms)  rollback transaction
ActiveModel::MissingAttributeError: can't write unknown attribute `book_id`
        from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4
.2.5.1/lib/active_record/attribute.rb:138:in `with_value_from_database'
        from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4
.2.5.1/lib/active_record/attribute_set.rb:39:in `write_from_user'
        from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4
.2.5.1/lib/active_record/attribute_methods/write.rb:74:in `write_attribute_with_
type_cast'

在这里，我试图通过插入一些数据将一个表(注释)与另一个表(图书)链接起来。我的代码流如下：

irb(main):004:0>book=Book.find(1)
comment = Comment.new :text => "This is an comment", :author => "Adam"
book.comments << comment

.......create_comments.rb：

class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.text :text
      t.string :author
      t.timestamps null: false
    end
  end
end

book.rb：

class Book < ActiveRecord::Base
    has_many :comments
end

comment.rb：

class Comment < ActiveRecord::Base
    belongs_to :book
end

在执行最后一行时，会出现此错误。

Answer 1

注释表中没有book_id列。

遵循以下步骤：

1. rails g migration AddBookToComments book:references

它将创建一个迁移文件，如下所示：

class AddBookToComments < ActiveRecord::Migration
  def change
    add_reference :comments, :book, index: true, foreign_key: true
  end
end

1. 运行rake db:migrate
2. 在comments_controller.rb中的强参数中添加book_id

然后试着：

> book=Book.find(1)
> comment = book.comments.new(:text => "This is an comment", :author => "Adam")
> comment.save!