Ruby on rails 通过多态关联创建对象

我需要（或者我认为）在我的模型中实现多态关联，但我出了点问题。让我们看看我的情况，这是一个简单的问答系统，逻辑如下： -一个问题可以由N个答案来回答。 -答案只能是一个“文本”异或（一个或另一个，而不是两个）一个“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

...
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
...

...
<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>
...

和视图表单（仅具有这些字段）：

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

...
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
...

...
<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>
...

。。。


真}）%%>


...

所以，问题是当我提交表单时，我会出现以下错误：

nil:NilClass的未定义方法

new'
app/controllers/answers\u controller.rb:52:in

create'

---

答案：）

在

有一个关系时，您必须使用：

@answerable.build_answer

或

而不是

@answerable.answer.new

请参阅以获取更多信息。
Hmm不确定它是否相关，但我会使用
attr\u accessible:answerable\u type，：answerable\u id
create方法中create\u answerable后@answerable.answer.class返回什么？@awenkh create\u answerable根据at参数type（“text”）创建继承类（AnswerText或AnswerPicture）的实例，或“图片”）。尝试将
create\u answerable（post[：answerable\u type]，post[：answerable]）
更改为
@answerable=create\u answerable（post[：answerable\u type]，post[：answerable]）
谢谢，你说得对。如果答案可能已经存在，我必须使用@answerable.create_-answer。并尝试（@answerable.answer | |@answerable.create_-answer）
@answerable.answer.new