我需要(或者我认为)在我的模型中实现多态关联,但我有问题。看我的情况,就是一个简单的问答系统,逻辑如下: - 一个问题可以用 N 个答案来回答。 - 答案只能是“文本”异或(一个或另一个,不能同时是两个)“图片”。
迁移:
class CreateAnswers < ActiveRecord::Migration
def change
create_table :answers do |t|
t.integer :question_id
t.references :answerable, :polymorphic => true
t.timestamps
end
end
end
class CreateAnswerTexts < ActiveRecord::Migration
def change
create_table :answer_texts do |t|
t.text :content
t.timestamps
end
end
end
class CreateAnswerPictures < ActiveRecord::Migration
def change
create_table :answer_pictures do |t|
t.string :content
t.timestamps
end
end
end
模型 *answer.rb*
class Answer < ActiveRecord::Base
belongs_to :user_id
belongs_to :question_id
belongs_to :answerable, :polymorphic => true
attr_accessible :answerable_type
end
answer_text.rb
class AnswerText < ActiveRecord::Base
TYPE = "text"
has_one :answer, :as => :answerable
attr_accessible :content
end
answer_picture.rb
class AnswerPicture < ActiveRecord::Base
TYPE = "picture"
has_one :answer, :as => :answerable
attr_accessible :content
end
Controller answers_controller.rb:
...
def create
post = params[:answer]
create_answerable(post[:answerable_type], post[:answerable])
@answer = @answerable.answer.new()
end
private
def create_answerable(type, content)
@answerable = ('Answer' + type.capitalize).classify.constantize.new(:content => content)
@answerable.save
end
...
和查看表单(只有这些字段):
...
<div class="field">
<%= f.label :answerable_type %><br />
<%= select("answer", "answerable_type", Answer::Types, {:include_blank => true}) %>
</div>
<div class="field">
<%= f.label :answerable %><br />
<%= f.text_field :answerable %>
</div>
...
所以,问题是当我提交表单时出现此错误:
undefined method
new' for nil:NilClass app/controllers/answers_controller.rb:52:in
create'
答案? :)
最佳答案
在 has_one
关系中,你必须使用:
@answerable.build_answer
或
@answerable.create_answer
代替
@answerable.answer.new
参见 the reference了解更多信息。
关于ruby-on-rails - 通过多态关联 rails 创建对象,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13351467/