Rails4 の form_for は multipart: true を省略可能 - Qiita

<%= form_for(@post) do |f| %> <% if @post.errors.any? %> <div id="error_explanation"> <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2> <ul> <% @post.errors.full_messages.each do |message| %> <li><%= message %></li> <% end %> </ul> </div> <% end %> <div class="field"> <%= f.label :title %><br> <%= f.text_field :title %> </div> <div class="field"> <%= f.l