STI和form_for问题

Question

我使用单表继承来管理不同类型的项目.

楷模:

class Project < ActiveRecord::Base
end

class SiteDesign < Project
end

class TechDesign < Project
end

从projects_controller编辑动作:

def edit
   @project = Project.find(params[:id])
end

查看edit.html.erb:

<% form_for(@project, :url => {:controller => "projects",:action => "update"}) do |f| %>
    ...
    <%= submit_tag 'Update' %>
<% end %>

更新projects_controller的操作:

def update
    @project = Project.find(params[:id])
    respond_to do |format|
      if @project.update_attributes(params[:project])
        @project.type = params[:project][:type]
        @project.save
        flash[:notice] = 'Project was successfully updated.'
        format.html { redirect_to(@project) }
        format.xml  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @project.errors, :status => :unprocessable_entity }
      end
    end
  end

然后我在编辑视图上对TechDesign条目进行一些编辑并获得错误:

NoMethodError in ProjectsController#update

You have a nil object when you didn't expect it!
You might have expected an instance of ActiveRecord::Base.
The error occurred while evaluating nil.[]

在参数中很明显,我没有项目参数名称,我有tech_design参数:

{"commit"=>"Update",
 "_method"=>"put",
 "authenticity_token"=>"pd9Mf7VBw+dv9MGWphe6BYwGDRJHEJ1x0RrG9hzirs8=",
 "id"=>"15",
 "tech_design"=>{"name"=>"ech",
 "concept"=>"efds",
 "type"=>"TechDesign",
 "client_id"=>"41",
 "description"=>"tech"}}

怎么解决？

Answer 1

这是你问题的根源.这是将@project设置为TechDesign对象的实例.

def edit
   @project = Project.find(params[:id])
end

您可以通过在form_for调用中指定:project作为名称来确保事情按您所需的方式工作.

<% form_for(:project, @project, :url => {:controller => "projects",:action => "update"}) do |f| %>
    ...
    <%= submit_tag 'Update' %>
<% end %>

Answer 2

对于Rails 3

<% form_for(@project, :as => :project, :url => {:controller => "projects",:action => "update"}) do |f| %>
...
   <%= submit_tag 'Update' %>
<% end %>