默认情况下 simple_form - collection_check_boxes 在末尾显示 hidden_field答案

【问题标题】：By default simple_form - collection_check_boxes displays hidden_field at the end默认情况下 simple_form - collection_check_boxes 在末尾显示 hidden_field
【发布时间】：2013-12-23 13:20:14
【问题描述】：

我在 new.html.erb 中使用 simple_form 的 collection_check_boxes。默认情况下，当呈现 html 时，它会在末尾添加隐藏字段，因为在控制器端我得到了最后一个元素为“”的值数组。谁能帮助我如何防止隐藏字段在视图上呈现？

new.html.erb：

<%= f.collection_check_boxes :topic_id, Topic.all, :id, :name %>
<%= f.button :submit %>

我使用 Firebug 检查了我的复选框元素，结果如下：

    <span>
    <span>
    <input type="hidden" value="" name="revision[topic_id][]">
    <input class="btn" type="submit" value="Create Revision" name="commit">

我想删除上面的隐藏字段。请帮忙。

【问题讨论】：

为什么要删除它？据我了解，这是为了涵盖您根本没有选择任何复选框的情况......
我基本上需要使用那些topic_ids并对其执行计数和类似功能。如果我有一个空字符串，那么我必须在使用它之前设置一个条件或将其弹出。但基本上我想知道目的。谢谢你:)

标签： ruby-on-rails checkbox ruby-on-rails-4 simple-form

【解决方案1】：

对于那些确实想要删除空值的人，请使用include_hidden: false param：

<%= f.collection_check_boxes :topic_id, Topic.all, :id, :name, include_hidden: false %>

它目前没有记录在 API 中，但它在那里：https://github.com/rails/rails/blob/master/actionview/lib/action_view/helpers/tags/collection_check_boxes.rb

      # Append a hidden field to make sure something will be sent back to the
      # server if all check boxes are unchecked.
      if @options.fetch(:include_hidden, true)
        rendered_collection + hidden_field
      else
        rendered_collection
      end

【讨论】：

【解决方案2】：

隐藏字段是故意存在的，您可能不想删除它。用于处理没有选中复选框的情况。

我认为 simple_form 最终会退回到标准 FormBuilder 中相同的基本 check_box 逻辑。以下是有关复选框为何具有该隐藏字段的一些文档。来自check_box documentation：

# The HTML specification says unchecked check boxes are not successful, and
# thus web browsers do not send them. Unfortunately this introduces a gotcha:
# if an +Invoice+ model has a +paid+ flag, and in the form that edits a paid
# invoice the user unchecks its check box, no +paid+ parameter is sent. So,
# any mass-assignment idiom like
#
#   @invoice.update(params[:invoice])
#
# wouldn't update the flag.
#     
# To prevent this the helper generates an auxiliary hidden field before
# the very check box. The hidden field has the same name and its
# attributes mimic an unchecked check box.
#
# This way, the client either sends only the hidden field (representing
# the check box is unchecked), or both fields. Since the HTML specification
# says key/value pairs have to be sent in the same order they appear in the
# form, and parameters extraction gets the last occurrence of any repeated
# key in the query string, that works for ordinary forms.

标准collection_check_boxes的example显示隐藏字段：

# Sample usage (selecting the associated Author for an instance of Post, <tt>@post</tt>):
#   collection_check_boxes(:post, :author_ids, Author.all, :id, :name_with_initial)
#
# If <tt>@post.author_ids</tt> is already <tt>[1]</tt>, this would return:
#   <input id="post_author_ids_1" name="post[author_ids][]" type="checkbox" value="1" checked="checked" />
#   <label for="post_author_ids_1">D. Heinemeier Hansson</label>
#   <input id="post_author_ids_2" name="post[author_ids][]" type="checkbox" value="2" />
#   <label for="post_author_ids_2">D. Thomas</label>
#   <input id="post_author_ids_3" name="post[author_ids][]" type="checkbox" value="3" />
#   <label for="post_author_ids_3">M. Clark</label>
#   <input name="post[author_ids][]" type="hidden" value="" />

【讨论】：

嘿，谢谢 :) 我基本上想知道文档的原因，而这正是你所做的。