ruby-on-rails – 为什么我得到’nil’不是与ActiveModel兼容的

nil is not an ActiveModel-compatible object. It must implement :to_partial_path.

我认为错误可能与我正在使用的教程有关,当我使用Rails 4时使用Rails 3.2.

这是型号代码：

class DashboardsController < ApplicationController
  def show
    @text_shout = TextShout.new
    @photo_shout = PhotoShout.new
    @shouts = current_user.shouts
  end
end

class PhotoShoutsController < ApplicationController
  def create
    content = build_content
    shout = current_user.shouts.build(content: content)
    if shout.save
      redirect_to dashboard_path
    else
      flash.alert = "Could not shout."
      redirect_to dashboard_path
    end
  end

  private
  def build_content
    PhotoShout.new(photo_shout_parameters)
  end

  def photo_shout_parameters
    params.require(:photo_shout).permit(:image)
  end
end

这是在_shout.html partial上发生错误的视图代码

# app/view/dashboards/show.html.erb
<%= form_for @text_shout do |form| %>
   <%= form.text_field :body,placeholder: 'Shout content here' %>
   <%= form.submit 'Shout' %>
<% end %>

<%= form_for @photo_shout do |form| %>
   <%= form.file_field :image %>
   <%= form.submit 'Shout' %>
<% end %>

<%= render @shouts %>

# app/view/shouts/_shout.html.erb
<%= div_for shout do %>
  <%= link_to shout.user.username,shout.user %>
  shouted
                                 +---------------------------------+
  <%= render shout.content %> <--| ERROR "nil' is not an Active "  |
                                 | "Model-compatible object"       |
                                 +---------------------------------+
  <%= link_to time_ago_in_words(shout.created_at),shout %>
<% end %>

# app/views/photo_shouts/_photo_shout.html.erb
<%= image_tag photo_shout.image.url(:shout) %>