Rails 3：Model.all => NoMethodError：undefined方法'接受'为零：NilClass

我试图围绕预先存在的MySQL数据库构建Rails应用程序。我创建了rails项目，正确设置了database.yml文件并创建了一个模型User，以便与db中的我的用户表相对应。当我运行轨道控制台然而测试出来，这就是我得到：Rails 3：Model.all => NoMethodError：undefined方法'接受'为零：NilClass

> User.all 
(32.4ms) SHOW TABLES 
(34.9ms) describe `users` 
NoMethodError: undefined method `accept' for nil:NilClass 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:7:in `to_sql' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:16:in `select_all' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/querying.rb:38:in `block in find_by_sql' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/explain.rb:40:in `logging_query_plan' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/querying.rb:37:in `find_by_sql' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/relation.rb:170:in `exec_queries' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/relation.rb:159:in `block in to_a' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/explain.rb:33:in `logging_query_plan' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/relation.rb:158:in `to_a' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/relation/finder_methods.rb:159:in `all' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/querying.rb:5:in `all' 
from (irb):1 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/console.rb:47:in `start' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/console.rb:8:in `start' 
from /home/richard/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands.rb:41:in `<top (required)>' 
from script/rails:6:in `require' 
from script/rails:6:in `<main>'1.9.3-p0 :002 > ^C

任何想法，这可能是为什么？据我所知，我遵循Rails约定：我使User模型与db中已经存在的称为用户的表相对应，其主键是一个名为id的整数字段。

来源

2012-02-15 Richard Stokes

你有一些名为'visitor'的列吗？ – shingara 2012-02-15 15:50:35

@shingara不，我不知道，为什么？ – 2012-02-15 16:12:51

，因为它是一个变量调用'visitor'在堆栈跟踪中是零。所以可能是问题 – shingara 2012-02-15 16:18:14

刚刚有同样的问题。由于它仅在分段环境（MySQL）中发生，而不是在开发环境（sqlite3）中发生，因此将其缩小为与MySQL相关的问题。通过将mysql2从版本0.2.7升级到0.3.11来修复它。

来源

2012-02-16 09:31:58 Ecco

这对我有用。编辑好的Gemfile删除版本'<0.3'。然后调用'bundle update mysql2'并用'rake db：drop'重新创建数据库，后跟'rake --trace db：setup'。 – peterept 2012-03-07 21:56:39

我在非Rails应用程序中使用0.3.11，并且仍然存在此问题。 – 2013-02-26 22:06:30

@BenHamill，我也有这个问题0.3.11，非Rails。通过从我的gemspec中删除activerecord-mysql2-adapter来解决它。 – 2013-07-10 21:18:32

升级到rails 3.2.2后，我有类似的问题与MySQL。

这是我所做的修复它。

rvm gem install mysql2 
In GemFile remove old MySQL gem and add - gem ‘mysql2' 
bundle install 
bundle update activerecord-mysql2-adapter 
bundle update mysql2

然后重新启动您的Rails服务器。

来源

2012-04-18 04:13:40

Rails 3：Model.all => NoMethodError：undefined方法'接受'为零：NilClass

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