使用has_many通过关联创建NoMethodError(未定义的方法`name'代表nil:NilClass)

我正在做这个教程,并且陷入了标记部分.基本上我有文章可以有一个标签列表.由于一篇文章可以有多个标签,反之亦然,因此还有一个额外的taggings模型,通过该模型建立这种关联.以下是模型:

class Article < ActiveRecord::Base
    has_many :comments
    has_many :taggings
    has_many :tags, through: :taggings
end

class Tag < ActiveRecord::Base
    has_many :taggings
    has_many :articles, through: :taggings
end

class Tagging < ActiveRecord::Base
    belongs_to :tag
    belongs_to :article
end

和迁移:

def change
    create_table :articles do |t|
        t.string :title
        t.text :body
        t.timestamps
    end

    create_table :tags do |t|
        t.string :name
        t.timestamps
    end

    create_table :taggings do |t|
        t.references :tag, index: true
        t.references :article, index: true
        t.timestamps
    end

还有article_controller(其中包括):

def create
    @article = Article.new(article_params)
    @article.save

    redirect_to article_path(@article)
end

现在,正如教程所说,当我尝试tag使用rails控制台为文章创建一个新的时,我得到NoMethodError一个nil:NilClass:

head :011 > Article.first.tags.create(name: "tag")
  Article Load (0.5ms)  SELECT "articles".* FROM "articles" ORDER BY "articles"."id" ASC LIMIT 1
  (0.2ms)  begin transaction
  SQL (0.8ms)  INSERT INTO "tags" ("created_at", "name", "updated_at") VALUES (?, ?, ?)  [["created_at", ...], ["name", "tag"], ["updated_at", ...]]
  SQL (2.1ms)  INSERT INTO "taggings" ("article_id", "created_at", "tag_id", "updated_at") VALUES (?, ?, ?, ?)  [["article_id", 1], ["created_at", ...], ["tag_id", 7], ["updated_at", ...]]
 (0.6ms)  rollback transaction
NoMethodError: undefined method `name' for nil:NilClass

所以在我看来,好像tag创建了条目,以及正确的taggings条目,但显然在某些时候它很难找到正确的tag,因此错误.我对吗？我怎样才能解决这个问题？

关于这种错误,我在SO上发现了很多问题,但每个问题都是由于我无法与之相关的一些问题引起的......

更新:

reloading 或重新启动rails控制台无效.

这是错误回溯,路径为~/.rvm/gems/ruby-head/gems/activerecord-4.0.4/lib/active_record:

from path/associations/has_many_association.rb:81:in `cached_counter_attribute_name'
from path/associations/has_many_association.rb:77:in `has_cached_counter?'
from path/associations/has_many_association.rb:85:in `update_counter'
from path/associations/has_many_through_association.rb:66:in `insert_record'
from path/associations/collection_association.rb:463:in `block (2 levels) in create_record'
from path/associations/collection_association.rb:367:in `add_to_target'
from path/associations/collection_association.rb:461:in `block in create_record'
from path/associations/collection_association.rb:152:in `block in transaction'
from path/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
from path/connection_adapters/abstract/database_statements.rb:221:in `within_new_transaction'
from path/connection_adapters/abstract/database_statements.rb:213:in `transaction'
from path/transactions.rb:209:in `transaction'
from path/associations/collection_association.rb:151:in `transaction'
from path/associations/collection_association.rb:460:in `create_record'
from path/associations/collection_association.rb:121:in `create'
from path/associations/collection_proxy.rb:260:in `create'
from (irb):14
from ~/.rvm/gems/ruby-head/gems/railties-4.0.4/lib/rails/commands/console.rb:90:in `start'
from ~/.rvm/gems/ruby-head/gems/railties-4.0.4/lib/rails/commands/console.rb:9:in `start'
from /.rvm/gems/ruby-head/gems/railties-4.0.4/lib/rails/commands.rb:62:in `'
from bin/rails:4:in `require'
from bin/rails:4:in `
'

tschale.. 15

我通过切换ruby版本来实现它.我正在使用ruby-head,这是ruby 2.2.0dev.切换回来ruby-2.1.1,现在它可以正常工作.应该早点尝试过......

也许这可以帮助其他人面临类似的错误.