Ruby on Rails：NilClass:Class 的未定义方法“model_name”

Question

我正在尝试允许用户将项目输入数据库。其中一个字段允许他们为该项目输入多种技术。

这是我的项目控制器，新建和创建操作。

def new
    @project = Project.new

@all_technols = Technol.all

@project_technol = @project.projecttechnols.build

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @project }
    end
  end


def create

    @project = Project.new(params[:project])

params[:technols][:id].each do |technol|

if !technol.empty?

    @project.projecttechnols.build(:technol_id => technol)
end
end

end

这是我的多选技术下拉列表的新项目视图。

<%= fields_for(@project_technol) do |ab| %>

<div class="tech">
<%= ab.label "All Tech" %><br/>

<%= collection_select(:technols, :id, @all_technols, :id, :tech, {}, {:multiple => true} ) %>
</div>
<% end %>

目前，我有一个页面，用户可以在其中输入一项新技术。但我想将此选项移至创建新项目页面，在那里他们可以选择现有技术，或输入新的技术，或两者兼而有之，他们将与该项目一起保存。

编辑：更改问题，并添加模型文件

但是，当我尝试保存新项目时，出现此错误。

undefined method `model_name' for NilClass:Class

Extracted source (around line #233):

233: <%= fields_for(@project_technol) do |ab| %>
234: 
235: <div class="tech">
236: <%= ab.label "All Tech" %><br/>

project.rb

class Project < ActiveRecord::Base

  attr_accessible :tech


  has_many :projecttechnols
  has_many :technols, :through => :projecttechnols
end

technol.rb

class Technol < ActiveRecord::Base
  attr_accessible :tech

has_many :projecttechnols
has_many :projects, :through => :projecttechnols
end

projecttechnol.rb

class Projecttechnol < ActiveRecord::Base
  attr_accessible :project_id, :technol_id

belongs_to :technol
belongs_to :project
end

EDIT2：

def new
    @project = Project.new

@all_technols = Technol.all

#@project_technol = @project.projecttechnols.build


@project_technol = Projecttechnol.new

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @project }
    end
  end

Answer 1

参考this

改变

@project.projecttechnols.build

到

@project.technols.build

假设您有以下模型声明

项目.rb

has_many :technols

technols.rb

belongs_to :project_id