轨道 - 活动记录 "RuntimeError: can't modify frozen String"与表单生成器有某种关系？

Question

当我提交表格更新我的模型时，我在浏览器中收到了这个错误：

ActiveRecord::StatementInvalid in CoachesController#update
RuntimeError: can't modify frozen String: INSERT INTO "availabilities" ("coach_id", "created_at", "day", "hour", "updated_at") VALUES (?, ?, ?, ?, ?)

轨道控制台上写着：

(0.0ms)  begin transaction
Binary data inserted for `string` type on column `day`
SQL (0.5ms)  INSERT INTO "availabilities" ("coach_id", "created_at", "day", "hour", "updated_at") VALUES (?, ?, ?, ?, ?)  [["coach_id", 14], ["created_at", Mon, 27 Feb 2012 21:59:05 UTC +00:00], ["day", "Monday"], ["hour", 20], ["updated_at", Mon, 27 Feb 2012 21:59:05 UTC +00:00]]
RuntimeError: can't modify frozen String: INSERT INTO "availabilities" ("coach_id", "created_at", "day", "hour", "updated_at") VALUES (?, ?, ?, ?, ?)
(0.1ms)  rollback transaction
Completed 500 Internal Server Error in 25ms
ActiveRecord::StatementInvalid (RuntimeError: can't modify frozen String: INSERT INTO "availabilities" ("coach_id", "created_at", "day", "hour", "updated_at") VALUES (?, ?, ?, ?, ?)):
app/models/coach.rb:93:in `block (2 levels) in update_general_availability'
app/models/coach.rb:92:in `each'
app/models/coach.rb:92:in `block in update_general_availability'
app/models/coach.rb:91:in `each'
app/models/coach.rb:91:in `update_general_availability'
app/controllers/coaches_controller.rb:25:in `update'

经过大量的实验，我发现了如何解决这个错误，但不是为什么我会首先得到它。

我有两个模型：Coach和Availabilities，具有has_many和belongs_to关联。这是可用性表的模式：

# Table name: availabilities
#  id         :integer         not null, primary key
#  coach_id   :integer
#  day        :string(255)
#  hour       :integer

它存储了一周中的一天和一天中教练空闲的时间。

我在Coach模型中编写了两种方法，以便更容易地处理教练的每周可用性。它们使用嵌套的哈希表，因此您可以查询coach在给定时间是否空闲。（例如：general_availability["Thursday"]["12"] #=> true）

#coach.rb
class Coach < ActiveRecord::Base
  ...
  # Creates a hash table mapping day and hour to true if available then, false otherwise
  # Form is general_availability["day"]["hr"]. Per Availability model, "0" = midnight, and
  # day of the week is of the form "Monday" or "Tuesday".
  def general_availability
    h = Hash.new()
    %w(Monday Tuesday Wednesday Thursday Friday Saturday Sunday).each { |day| h[day] = Hash.new(false) }
    self.availabilities.each do |a|
      h[a.day][a.hour.to_s] = true
    end
    return h
  end
  # Takes a hash table of the kind returned by general_availability and updates
  # this coach's records in the Availabilities table
  def update_general_availability(ga_hash_table)
    self.availabilities.clear
    ga_hash_table.each do |day, hrs|
      hrs.each do |hr, val|
        self.availabilities.create({day: day, hour: hr.to_i})
      end
    end
  end

这是以表格形式显示教练每周可用性的部分。每一天/每一小时的单元格都是一个复选框，教练可以选中或取消选中该复选框以指示他们是否有空。

<!-- availabilities/_scheduler.html.erb -->
<h2>General Availability</h2>
Please check the times below that you would generally be available for a training session.
<table class="table" id="availabilities_table">
  <tr>
    <th>Time</th>
    <% days_of_the_week.each do |day| %> 
      <th><%= day %></th> 
    <% end %>
  </tr>
  <% (6..21).each do |hr| %>
    <tr>
      <td><%= format_as_time hr %></td>
      <% days_of_the_week.each do |day| %>
        <% is_checked = @general_availability[day][hr.to_s] %>
        <td class="availabilities_cell">
          <%= check_box_tag "availability[#{day}][#{hr}]", true, is_checked, :class => 'availabilities_check_box' %>
        </td>
      <% end %>
    </tr>
  <% end %>
</table>

这是控制器：

# coaches_controller.rb
...
def edit
  @coach = current_user.coach
  @general_availability = @coach.general_availability
end
def update
  @coach = Coach.find(params[:id])
  @coach.update_attributes(params[:coach])  
  if @coach.save
    @coach.update_general_availability(params[:availability])
    redirect_to @coach
  end
  # ...
end

这是线路

@coach.update_general_availability(params[:availability])

导致错误的。

现在，这是我的问题为什么此视图会导致上述错误

<!-- edit.html.erb version 1 -->
<h1><%= @coach.user.first_name %>  </h1>
<%= form_for @coach, :html => { :multipart => true } do |f| %> 
  <%= f.label :profile_photo %> 
  <%= f.file_field :profile_photo %> 
  <div class="field">
    <%= f.label :phone_number %>
    <%= f.text_field :phone_number %>
  </div>  
  ... More Form Fields Here ...
  <%= render 'availabilities/scheduler' %>
  <%= f.button %> 
<% end %> 

而此视图没有

<!-- edit.html.erb version 2 -->
<h1><%=  @coach.user.first_name %>  </h1>
<%= form_for @coach, :html => { :multipart => true } do |f| %> 
  <%= f.label :profile_photo %> 
  <%= f.file_field :profile_photo %> 
  <div class="field">
    <%= f.label :phone_number %>
    <%= f.text_field :phone_number %>
  </div>  
  ... More Form Fields Here ...
  <%= f.button %> 
<% end %> 
<%= form_for @coach, :class => "form-vertical" do |f| %>
  <%= render 'availabilities/scheduler' %>
  <%= submit_tag "Update Schedule" %>
<% end %>

请注意，在前者中，分部位于表单生成器表单内部，而在第二种情况中，分部在下面被呈现为其自己的form_for。

从我粘贴在上面的日志中跳出来的部分是这样的：

Binary data inserted for `string` type on column `day`

其在表单工作时（例如在表单的版本2中）不出现。这看起来很重要，但我不知道这意味着什么，也不知道为什么会发生。

非常感谢！

Answer 1

想明白了。Ruby哈希表键已冻结。所以我的参数看起来像：

params[:availability][:Thursday][:10] = "true"

当我的update_general_availability方法做到这一点时：

self.availabilities.create({day: day, hour: hr.to_i})

:day是"Thursday"，但SQLite适配器知道它有Encoding::ASCII_8BIT（也称为"二进制"），并尝试执行encode! 'utf-8'。然而，由于它被冻结，这引发了Runtime frozen String错误。通过将这些行添加到update_general_availability方法中解决了问题：

day = day.dup
hr = hr.dup

现在，由于它们是重复的，而不是散列密钥本身，所以它们可以被编码为utf-8。