非常简单的ruby on rails问题。我正在制作一个应用程序，其中有讨论，用户可以评论它们，我希望他们的gravatar出现在他们评论的一边。怎么会这样做呢？谢谢！
_discussion.html.erb
<% content_for :script do %>
<%= javascript_include_tag 'hover_content' %>
<% end %>
<% @micropost = Micropost.new %>
<% @micropost.discussion_id = discussion.id %>
<li>
<div class = "intro-bar"><span class = "intro"><%=discussion.intro %></span></div>
<div class = "content-bar">
<span class = "content"><%= discussion.content %></span>
</div>
<input type='button' id='hideshow' value='hide/show'>
<div class = "buttons">
<!--<div class = "vote-neg"><%= link_to "Break Up", signup_path,class: "btn btn-large btn-breakup" %></div>-->
<!--<div class = "vote-plus"><%= link_to "Stay Together", signup_path,class: "btn btn-large btn-staytogether" %></div>-->
</div>
</li>
<span class = "timestamp">
Posted <%= time_ago_in_words(discussion.created_at) %> ago.
</span>
<% if signed_in? %>
<div class = "row">
<aside class = "span4">
<section>
<%= form_for(@micropost) do |f| %>
<%= render 'shared/error_messages', object: f.object %>
<div class="field">
<%= f.text_area :content, placeholder: "Post a comment" %>
</div>
<%= f.hidden_field :discussion_id%>
<%= f.submit "Break Up", class: "btn btn-large btn-breakup",:name => "break_up" %>
<%= f.submit "Stay Together", class: "btn btn-large btn-staytogether", :name => "stay_together" %>
<% end %>
</section>
</aside>
</div>
<% end %>
<div class = "comments">
<% discussion.microposts.each do |micropost| %>
<li>
<div class = "comment-pic"></div>
<div class = "post-comment"><%= micropost.content%></div>
</li>
<% end %>
</div>
用户显示页面
<% provide(:title, @user.username) %>
<div class="row">
<aside class="span4">
<section>
<h1>
<%= gravatar_for @user %>
<%= @user.username %>
</h1>
</section>
</aside>
</div>
<div id = "user_content">
<p>
<%= @user.email %><br/>
<%= @user.age %> years old <br/>
<%= @user.sex %> <br/>
</p>
</div>
</div>