app/views/books/_form.html.erb
<%= form_for(@book) do |f| %>
<% if @book.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@book.errors.count, "error") %> prohibited this book from being saved:</h2>
<ul>
<% @book.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :title %><br />
<%= f.text_field :title %>
</div>
<div class="field">
<%= f.label :description %><br />
<%= f.text_area :description %>
</div>
<div class="field">
<%= f.label :image_url %><br />
<%= f.text_field :image_url %>
</div>
<div class="field">
<%= collection_select(:book, :lent_to_user_id, User.all, :id, :name, :prompt => true) %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>