fields_for 和参数数量错误（0 代表 1）错误

Question

业余 Rails 程序员努力使用 fields_for 表单生成器。我的 Rails 应用程序（v=2.3.11）跟踪实验室协议和这些协议中使用的动物（它们的体重等）。

我的具体问题是协议只能有一定数量的动物，但允许的数量是特定于某个物种的。

嵌套表单行为应显示所有动物物种的列表以及协议允许的数量的编辑框。

模型：协议、Allowed_Animal、物种

物种模型

class Species < ActiveRecord::Base
  has_many :animals, :order => "band"
  has_many :allowed_animals
end

协议模型

class Protocol < ActiveRecord::Base
  has_and_belongs_to_many :animals, :order => "band"
  has_many :allowed_animals
  accepts_nested_attributes_for :allowed_animals
end

Allowed_Animal 模型

class AllowedAnimal < ActiveRecord::Base
  belongs_to :protocol
  has_one :species
end

allowed_animal 的表格包括：

id, protocol_id, species_id, number, created_at, updated_at

嵌套表单的工作方式如下：

<% form_for(@protocol) do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :title %><br />
    <%= f.text_field :title %>
  </p>
  <p>
    <%= f.label :number %><br />
    <%= f.text_field :number %>
  </p>

  <p>
    Number of animals allowed on protocol:
  </p>
  <div class="left_indent">
    <table>
      <% f.fields_for :allowed_animals, Species.all do |a| %>
      <tr>
        <td><i><%= a.object[:name] %></i></td>
        <td><%= a.text_field :number, :value => @protocol.allowed_animals(a), :size=>2 %></td>
        <%= a.text_field :species_id, :value => a.object[:id], :hidden => true %>
      </tr>
      <% end %>
    </table>
  </div>

  <p>
    Users on protocol:
  </p>
  <div class="left_indent">
    <%= render :partial => 'protocols/users_on_protocol_form', :locals =>{:protocol => @protocol, :users => User.current} %>
  </div>

  <p>
    <%= f.submit 'Save' %>
  </p>
<% end %>

表单显示我希望如何，但提交后，我收到错误：

wrong number of arguments (0 for 1)

在控制器中尝试执行的操作：

@protocol = Protocol.new(params[:protocol])

我不知道从这里去哪里。我的模型中需要有构建方法吗？或者我需要在控制器中做一些特殊的事情吗？我的 form_builder 代码及其迭代物种的方式是否有问题？

有什么想法吗？

应用程序跟踪：

/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/nested_attributes.rb:343:in `allowed_animals'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/nested_attributes.rb:343:in `send'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/nested_attributes.rb:343:in `assign_nested_attributes_for_collection_association'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/nested_attributes.rb:244:in `allowed_animals_attributes='
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/base.rb:2918:in `send'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/base.rb:2918:in `assign_attributes'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/base.rb:2914:in `each'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/base.rb:2914:in `assign_attributes'
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/base.rb:2787:in `attributes='
/var/lib/gems/1.8/gems/activerecord-2.3.11/lib/active_record/base.rb:2477:in `initialize'
/media/Data/Animal-Record-Keeping/app/controllers/protocols_controller.rb:42:in `new'
/media/Data/Animal-Record-Keeping/app/controllers/protocols_controller.rb:42:in `create'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/base.rb:1333:in `send'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/base.rb:1333:in `perform_action_without_filters'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/filters.rb:617:in `call_filters'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/filters.rb:610:in `perform_action_without_benchmark'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/var/lib/gems/1.8/gems/activesupport-2.3.11/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/var/lib/gems/1.8/gems/activesupport-2.3.11/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/rescue.rb:160:in `perform_action_without_flash'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/flash.rb:151:in `perform_action'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/base.rb:532:in `send'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/base.rb:532:in `process_without_filters'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/filters.rb:606:in `process'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/base.rb:391:in `process'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/base.rb:386:in `call'
/var/lib/gems/1.8/gems/actionpack-2.3.11/lib/action_controller/routing/route_set.rb:438:in `call'

参数：

{"commit"=>"Save",
 "protocol"=>{"number"=>"Test number",
 "start_date(1i)"=>"2011",
 "start_date(2i)"=>"4",
 "title"=>"Test title",
 "start_date(3i)"=>"12",
 "flight_exempt"=>"0",
 "allowed_animals_attributes"=>{"0"=>{"number"=>"7",
 "id"=>"2",
 "species_id"=>"2"},
 "1"=>{"number"=>"11",
 "id"=>"3",
 "species_id"=>"3"},
 "2"=>{"number"=>"13",
 "id"=>"4",
 "species_id"=>"4"},
 "3"=>{"number"=>"17",
 "id"=>"5",
 "species_id"=>"5"}},
 "summary"=>"Test summary"},
 "user_id"=>{"33"=>"0",
 "6"=>"0",
 "14"=>"0",
 "9"=>"0",
 "37"=>"0",
 "38"=>"0",
 "1"=>"1",
 "39"=>"0",
 "40"=>"0",
 "18"=>"0",
 "31"=>"0",
 "21"=>"0",
 "32"=>"0",
 "5"=>"0"}}

开发日志

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Processing ProtocolsController#create (for 127.0.0.1 at 2011-04-12 18:11:43) [POST]
  Parameters: {"commit"=>"Save", "protocol"=>{"start_date(1i)"=>"2011", "number"=>"Test Number", "start_date(2i)"=>"4", "start_date(3i)"=>"12", "title"=>"Test Title", "allowed_animals_attributes"=>{"0"=>{"number"=>"7", "id"=>"2", "species_id"=>"2"}, "1"=>{"number"=>"11", "id"=>"3", "species_id"=>"3"}, "2"=>{"number"=>"13", "id"=>"4", "species_id"=>"4"}, "3"=>{"number"=>"17", "id"=>"5", "species_id"=>"5"}}, "flight_exempt"=>"0", "summary"=>"Test Summary"}, "user_id"=>{"6"=>"0", "33"=>"0", "9"=>"0", "14"=>"0", "37"=>"0", "38"=>"0", "40"=>"0", "39"=>"0", "1"=>"1", "18"=>"0", "31"=>"0", "32"=>"0", "21"=>"0", "5"=>"0"}}
::: Checking session expiry
::: Session has not expired. Reinitialising.
::: Initializing session expiry. Expires at Tue Apr 12 18:26:43 -0400 2011
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ArgumentError (wrong number of arguments (0 for 1)):
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  app/controllers/protocols_controller.rb:42:in `create'
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  /var/lib/gems/1.8/gems/ruby-debug-ide-0.4.9/bin/rdebug-ide:87
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  /var/lib/gems/1.8/bin/rdebug-ide:19

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Rendering rescues/layout (internal_server_error)

Answer 1

我发现问题是我的协议模型中有一个与我试图嵌套的模型同名的函数（AllowedAnimal）。当调用protocol.allowed_animals时，它正在调用函数（没有足够的参数）而不是返回嵌套的fields_for。

我还必须在我的允许的动物模型中更改与belongs_to的关系以使我的allowed_animal.species正常工作：

class AllowedAnimal < ActiveRecord::Base
  belongs_to :protocol
  belongs_to :species
end

并在我的模型中添加一个方法来为新协议构建allowed_animals：

def build_allowed_animals
  abs = Array.new
  for sp in Species.all
    ab = AllowedAnimal.new
    ab.species = sp
    ab.number = 0
    abs << ab
  end
  self.allowed_animals = abs
end

调用该方法在我的协议控制器中：

def new
  @protocol = Protocol.new
  @protocol.build_allowed_bats
  respond_to do |format|
    format.html # new.html.erb
    format.xml  { render :xml => @protocol }
  end
end

并对我的表单进行一些编辑：

<% form_for(@protocol) do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :title %><br />
    <%= f.text_field :title %>
  </p>
  <p>
    <%= f.label :number %><br />
    <%= f.text_field :number %>
  </p>

  <p>
    Number of animals allowed on protocol:
  </p>
  <div class="left_indent">
    <table>
      <% f.fields_for :allowed_animals do |a| %>
        <tr>
          <td><i><%= a.object.species.name %></i></td>
          <td><%= a.text_field :number, :value => @protocol.determine_allowed_animals(a.object.species), :size=>2 %></td>
          <%= a.text_field :species_id, :value => a.object.species.id, :hidden => true %>
        </tr>
      <% end %>
    </table>
  </div>

  <p>
    Users on protocol:
  </p>
  <div class="left_indent">
    <%= render :partial => 'protocols/users_on_protocol_form', :locals =>{:protocol => @protocol, :users => User.current} %>
  </div>

  <p>
    <%= f.submit 'Save' %>
  </p>
<% end %>

Answer 2

在 Rails 3 中，你应该这样写：

<%= f.fields_for :allowed_animals do |a| %>