ruby-on-rails - Rails - Active Record "RuntimeError: can' t 修改卡住字符串“与表单生成器有某种关系？

Question

当我提交表单以更新我的模型时，我在浏览器中收到此错误:

ActiveRecord::StatementInvalid in CoachesController#update

RuntimeError: can't modify frozen String: INSERT INTO "availabilities" ("coach_id", "created_at", "day", "hour", "updated_at") VALUES (?, ?, ?, ?, ?)

rails 控制台是这样说的:

(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'

经过大量试验后，我找到了解决此错误的方法，但不知道为什么我会首先遇到它。

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

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

它存储一周中的某一天和一天中教练有空的时间。

我在 Coach 模型中编写了两个方法来更轻松地处理教练的每周可用性。他们使用嵌套哈希表，因此您可以查询教练在给定时间是否有空。 (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

这是将教练的每周可用性显示为表格的部分。每个天/小时单元格都是一个复选框，教练可以选中或取消选中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 Controller :

# 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

是线

@coach.update_general_availability(params[:availability])

导致错误。

现在，这是我的问题。 为什么这个 View 会导致上面的错误？

<!-- 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 %> 

虽然这个观点没有？

<!-- 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，部分在表单构建器表单内，而在第二种情况下，部分在下面呈现为它自己的 form_for。

从我上面粘贴的日志中跳出来的部分是这一行:

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

在表单工作时不会出现(例如，在表单的版本 2 中)。这似乎很重要，但我不知道这意味着什么或为什么会发生。

非常感谢!

Answer 1

想通了。 Ruby 哈希表键被卡住。所以我的参数看起来像:

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

当我的 update_general_availability 方法执行此操作时:

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

:day 是 "Thursday"，但 SQLite 适配器将其理解为具有 Encoding::ASCII_8BIT(也称为“二进制”)，并尝试进行 编码! 'utf-8' 它。但是，由于它被卡住，因此引发了运行时卡住字符串错误。通过将这些行添加到 update_general_availability 方法解决了这个问题:

day = day.dup
hr = hr.dup

现在，因为它们是重复的而不是哈希键本身，所以它们可以编码为 utf-8。