rails中一个窗体多个模型——fields_for

详细参考

http://railscasts.com/episodes/73-complex-forms-part-1中part-1、2、3部分

借助field_for可以生成表单来处理两个或更多模型对象的数据

先看一个官方的例子，一个表单中有person和permission两个模型，其中每个person包含一个permission

<%= form_for(@person) do |person_form| %>
   First name: <%= person_form.text_field :first_name %>
   Last name: <%= person_form.text_field :last_name %>  

   <% fields_for :permission, @person.permission do |permission_fields| %>
     Admin : <%= permission_fields.check_box :admin %>
   <% end %>
 <% end %>  

当一个person包含多个permission时，view代码如下

<%= form_for(@person) do |person_form| %>
   First name: <%= person_form.text_field :first_name %>
   Last name: <%= person_form.text_field :last_name %>  

   <% for permission in @person.permissions %>
     <%= fields_for "permission[]", permission do |permission_fields| %>
       Admin : <%= permission_fields.check_box :admin %>
     <% end %>
   <% end %>
<% end %>  

1、其中"permission[]"保证了多个permission对象id不同，都包含在param[]中

2、此时，param[:person]={:first_name => v, :last_name => v, :permission1=>v, :permission2 => v...}

3、<%=person_form.fields_for "permission[]", permission do |permission_fields| %>时，

param[:person]={:first_name => v, :last_name => v, :persom=>{:permission1=>v, :permission2 => v...}}

model代码

# models/.person.rb
def permission_attributes=(permission_attributes)
  permission_attributes.each do |attributes|
    permissions.build(attributes)
  end
end  

为了对应view里面的permission[]

controller里的create方法

# persons_controller.rb
def new
  @person= person.new
  3.times { @person.permissions.build }
end  

def create
  @person= Person.new(params[:project)
  if @person.save
    flash[:notice] = "Successfully created project."
    redirect_to persons_path
  else
    render :action => 'new'
  end
end