创建新记录获取 NameError：未定义的局部变量或方法"通过"

Question

我是Rails的新手，我遵循Railscast #258实现jQuery TokenInput，由于某种原因，在尝试创建一个新记录时，我得到了错误:

NameError: undefined local variable or method `through' for #<Class:0x101667ef0>
    from /Library/Ruby/Gems/1.8/gems/activerecord-3.0.5/lib/active_record/base.rb:1008:in `method_missing'
    from /Users/Travis/Desktop/YourTurn/app/models/tag.rb:4
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:454:in `load'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:454:in `load_file'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:596:in `new_constants_in'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:453:in `load_file'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:340:in `require_or_load'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:491:in `load_missing_constant'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:183:in `const_missing'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:181:in `each'
    from /Library/Ruby/Gems/1.8/gems/activesupport-3.0.5/lib/active_support/dependencies.rb:181:in `const_missing'

My Tags controller:

class TagsController < ApplicationController
def index
    @tags = Tag.where("name like ?", "%#{params[:q]}%")
    respond_to do |format|
      format.html
      format.json { render :json => @tags.map(&:attributes) }
    end
  end
  def show
    @tag = Tag.find(params[:id])
  end
  def new
    @tag = Tag.new
  end
  def create
    @tag = Tag.new(params[:tagging])
    if @tag.save
      redirect_to @tag, :notice => "Successfully created tag."
    else
      render :action => 'new'
    end
  end

标记方法:

class Tag < ActiveRecord::Base
  attr_accessible :name
  has_many :taggings
  has_many :questions, through => :taggings
end

标记方法:

class Tagging < ActiveRecord::Base
  attr_accessible :question_id, :tag_id
  belongs_to :question
  belongs_to :tag
end

方法with:through:

  has_many :taggings
  has_many :tags, :through => :taggings
  attr_reader :tag_tokens

如果我在终端中创建tag = Tagging.new，我得到适当的条目，但不是我在db迁移create_tags中的标记名称。谁能帮我弄清楚是什么问题吗?如果我需要提供其他代码，我很乐意。

Answer 1

你少了一个冒号，这:

class Tag < ActiveRecord::Base
  attr_accessible :name
  has_many :taggings
  has_many :questions, through => :taggings
end

应该是这样的:

class Tag < ActiveRecord::Base
  attr_accessible :name
  has_many :taggings
  has_many :questions, :through => :taggings
end

注意through变为:through。只有through是一个变量，但:through是一个符号，这是你通常想要的构建哈希