Rails 3-嵌套模型的JSON没有按预期返回

我正试图在中设置一个javascript前端，该前端使用Rails后端的JSON。

唯一的问题是，当我在Rails中嵌套模型时，我不确定返回的JSON格式是否正确。

我有一个Post模型和一个Comment模式。一篇帖子有很多评论。每个模型都有一个"title"answers"content"字段。

到目前为止，我的问题就在这里。。。

1）当我访问url:http://localhost:3000/posts.json时，我会得到预期的输出：

> [{"content":"My first
> post","created_at":"2012-02-07T18:56:16Z","id":1,"title":"Hello","updated_at":"2012-02-07T18:56:16Z"},{"content":"More
> crap","created_at":"2012-02-07T21:30:51Z","id":2,"title":"My 2nd
> Post","updated_at":"2012-02-07T21:30:51Z"}]

2）如果我输入这个url:http://localhost:3000/posts/1/comments/4.json，我也会得到预期的：

> {"content":"that's
> nice","created_at":"2012-02-07T20:57:16Z","id":4,"post_id":1,"title":"cool","updated_at":"2012-02-07T20:57:16Z"}

3）但是。。。如果我放入这样的url：http://localhost:3000/posts/1/comments.json

则返回null。

我无法访问与帖子相关联的评论列表的JSON版本。

使用标准的Rails视图，我可以在嵌套的情况下完成完整的CRUD，这没有问题，但为了在客户端使用JSON，我是否需要做一些与Rails通常传递JSON的方式不同的事情

编辑

我假设您可能需要查看注释控制器的控制器代码。这是：

class CommentsController < ApplicationController
  before_filter :get_post  
  respond_to :html, :xml, :json
  def index
    @comments = @post.comments.all    
    respond_with (@comment)    
  end
  def show
    @comment = @post.comments.find(params[:id])
    respond_with(@comment)
  end
  def new
    @comment = @post.comments.build
    respond_with(@comment)
  end
  def edit
    @comment = @post.comments.find(params[:id])
  end
  def create
    @comment = @post.comments.build(params[:comment])
    respond_to do |format|
      if @comment.save
        format.html { redirect_to([@post, @comment], :notice => 'Comment was successfully created.') }
        format.xml  { render :xml => @comment, :status => :created, :location => @comment }
        format.json  { render :json => @comment, :status => :created, :location => @comment }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @comment.errors, :status => :unprocessable_entity }
        format.json  { render :json => @comment.errors, :status => :unprocessable_entity }
      end
    end
  end
 def update
    @comment = @post.comments.find(params[:id])
    respond_to do |format|
      if @comment.update_attributes(params[:comment])
        format.html { redirect_to(@comment, :notice => 'Comment was successfully updated.') }
        format.xml  { head :ok }
        format.json  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @comment.errors, :status => :unprocessable_entity }
        format.json  { render :json => @comment.errors, :status => :unprocessable_entity }
      end
    end
  end
  def destroy
    @comment = @post.comments.find(params[:id])
    @comment.destroy
    respond_to do |format|
      format.html { redirect_to(post_comments_url) }
      format.xml  { head :ok }
      format.json  { head :ok }
    end
  end  
  protected  
  def get_post
    @post = Post.find_by_id(params[:post_id])
    redirect_to root_path unless @post
  end
end