rails 复选框 check_box_tag

<%= error_messages_for 'product' %>

<p>
  Name<br/>
  <%= text_field :product, :name %>
</p>

<p>
  Price<br/>
  <%= text_field :product, :price %>
</p>

<p>
  <% for category in Category.find(:all) %>
  <div>
    <%= check_box_tag "product[category_ids][]", category.id, @product.categories.include?(category) %>
    <%= category.name %>
  </div>
  <% end %>
</p>

check_box_tag 'accept'
# => <input id="accept" name="accept" type="checkbox" value="1" />

check_box_tag 'rock', 'rock music'
# => <input id="rock" name="rock" type="checkbox" value="rock music" />

check_box_tag 'receive_email', 'yes', true
# => <input checked="checked" id="receive_email" name="receive_email" type="checkbox" value="yes" />

check_box_tag 'tos', 'yes', false, class: 'accept_tos'
# => <input class="accept_tos" id="tos" name="tos" type="checkbox" value="yes" />

check_box_tag 'eula', 'accepted', false, disabled: true
# => <input disabled="disabled" id="eula" name="eula" type="checkbox" value="accepted" />

通过 value 的值可判断check_box是否存在