升级到 mongoid 5.0.2：ArgumentError：Fixnum 与 nil 的比较失败答案

【问题标题】：Upgrading to mongoid 5.0.2: ArgumentError: comparison of Fixnum with nil failed升级到 mongoid 5.0.2：ArgumentError：Fixnum 与 nil 的比较失败
【发布时间】：2016-01-08 12:46:01
【问题描述】：

我正在尝试在我的 Rails 应用中升级 Mongoid。

我的 Gemfile 现在包含：

mongoid 5.0.2 (was 4.0.0)
bson 4.0.0 (was 2.3.0)
moped 1.5.3 (was 2.0.2)
mongo 2.2.1
rails 4.2.3

根据the Docs，我已更新mongoid.yml 以反映所需的更改：

development:
  clients:
    default:
      database: my_db_name
      hosts:
        - localhost:27017
      options:
  options:

我的application.rb 看起来像这样：

require File.expand_path('../boot', __FILE__)
require "action_controller/railtie"
require "action_mailer/railtie"
require "sprockets/railtie"
Bundler.require(:default, Rails.env)

module MyApp
  class Application < Rails::Application

    config.autoload_paths += %W(#{config.root}/lib)
    config.autoload_paths += Dir[Rails.root.join('app', 'models', '{**}')]

    config.generators do |g|
      g.orm :mongoid
    end
  end
end

但是现在，每当我尝试连接数据库时，我都会得到这个堆栈跟踪：

ArgumentError: comparison of Fixnum with nil failed
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/protocol/message.rb:117:in `>'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/protocol/message.rb:117:in `deserialize'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connectable.rb:107:in `block in read'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connectable.rb:91:in `ensure_connected'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connectable.rb:106:in `read'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connection.rb:180:in `deliver'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connection.rb:125:in `block in dispatch'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/monitoring/publishable.rb:47:in `publish_command'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connection.rb:124:in `dispatch'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/operation/executable.rb:36:in `block in execute'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/connection_pool.rb:108:in `with_connection'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/server/context.rb:63:in `with_connection'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/operation/executable.rb:34:in `execute'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/database.rb:158:in `command'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/collection/view/readable.rb:136:in `block in count'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/retryable.rb:51:in `call'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/retryable.rb:51:in `read_with_retry'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongo-2.2.1/lib/mongo/collection/view/readable.rb:135:in `count'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongoid-5.0.2/lib/mongoid/contextual/mongo.rb:59:in `block in count'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongoid-5.0.2/lib/mongoid/contextual/mongo.rb:488:in `try_cache'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongoid-5.0.2/lib/mongoid/contextual/mongo.rb:59:in `count'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongoid-5.0.2/lib/mongoid/contextual/mongo.rb:86:in `destroy'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/mongoid-5.0.2/lib/mongoid/contextual.rb:20:in `destroy'
  from (irb):1
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/railties-4.2.3/lib/rails/commands/console.rb:110:in `start'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/railties-4.2.3/lib/rails/commands/console.rb:9:in `start'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:68:in `console'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
  from /Users/me/.rvm/gems/ruby-2.1.2@my-app/gems/railties-4.2.3/lib/rails/commands.rb:17:in `<top (required)>'
  from bin/rails:4:in `require'
  from bin/rails:4:in `<main>'2.1.2

另外，当我查看服务器日志时，每隔 30 秒左右就会添加一个新行，其中包含以下文本：

MONGODB | wrong number of arguments (1 for 0)

知道为什么会这样吗？

【问题讨论】：

标签： ruby-on-rails ruby mongodb mongoid

【解决方案1】：

您的 ruby 版本似乎早于 2.2.1，从 mongo-ruby-driver backtrace 来看，它可能需要 ruby 2.2.1+。

Error backtrace

Possible culprit, MAX_MESSAGE_SIZE is nil

【讨论】：

我在ruby 2.1.2p95 上运行，所以我现在将尝试更新它。但是，我确实有另一个应用程序在 ruby 2.0.0p247 上运行，带有新的 Mongoid/Mongo 版本。
String freeze 默认行为可能在 2.0 - 2.1 - 2.2 之间发生了变化，尝试升级是否有效，或者尝试将 MONGO gem 降级到 2.2.0。 Mongoid 需要 MONGO >= 2.1，所以这应该可以正常工作。
降级到 mongo v. 2.1.2 并将 Ruby 升级到 v. 2.2.2 成功了。谢谢。