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环境：
ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin11.4.0]
rvm 1.14.5 (stable) by Wayne E. Seguin <[email protected]>, Michal Papis <[email protected]> [https://rvm.io/]
Rails 3.2.6
MongoDB db version v2.0.6, pdfile version 4.5
终端中执行命令：
rails new mongodemo
gem install mongo_mapper
在enviroment.rb中添加config.gem "mongo_mapper"
如启动报config变量无法找到，则修改config.gem "mongo_mapper"为$config.gem "mongo_mapper"
异常信息：
/Users/seraph/Documents/rails_projects/mongodemo/config/environment.rb:7:in `<top (required)>': undefined local variable or method `config' for main:Object (NameError)
$config代表全局变量引用
在config/initalizers中添加文件mongo_config.rb
内容：MongoMapper.database = "mongodemo-#{Rails.env}"
在Gemfile中添加
source "http://gemcutter.org"
gem 'mongo_mapper', github: "jnunemaker/mongomapper"
gem "bson_ext"
gem "nifty-generators", :group => :development
然后执行命令：bundle install
使用脚手架，生成MongoDB演示代码：
rails generate scaffold project name:string --orm=mongo_mapper
rails generate scaffold task project_id:string name:string completed:boolean --orm=mongo_mapper
访问MongoDB: http://localhost:28017/
各种异常情况处理：
1.问题：启动Rails服务器如报如下异常，说明没有安装bson_ext.
gem install bson_ext
If you continue to receive this message after installing, make sure that the
bson_ext gem is in your load path and that the bson_ext and mongo gems are of the same version.
2.问题：在使用nifty生成代码时，如报如下异常，需执行：gem install nifty-generators
rails g nifty:scaffold Recipe name:string index new
/Users/seraph/.rvm/gems/ruby-1.9.3-p194@global/gems/bundler-1.1.4/lib/bundler/resolver.rb:287:in `resolve': Could not find gem 'nifty-generators (>= 0) ruby' in the gems available on this machine. (Bundler::GemNotFound)
3.问题：mongodb演示，访问http://localhost:3000/projects时，报异常：undefined method `key?' for nil:NilClass
解决：
（1）在Gemfile中添加
（2）在终端中运行
bundle install
解释：
Explanation: Rails 3.2.4 added a accessible_attributes method to ActiveModel, but MongoMapper already had this; so they were clobbering each other.
4.问题：访问http://localhost:3000/projects时，报如下异常：
ArgumentError (wrong number of arguments (1 for 0)):
app/controllers/projects_controller.rb:1:in `<top (required)>'
解决办法：未能明确，怀疑
5.问题：如果访问MongoDBhttp://localhost:28017/页面时，页面提示需开启rest，则在/usr/local/mongodb/mongod.conf文件中添加
rest = true
全部内容是：
# Store data alongside MongoDB instead of the default, /data/db/
dbpath = /usr/local/mongodb_data
# Only accept local connections
bind_ip = 127.0.0.1
# Seraph add, to enable REST
rest = true
资源：
Rails + MongoDB的Demo开发: http://railscasts.com/episodes/194-mongodb-and-mongomapper?autoplay=true
在Mac环境下安装MongoDB: http://shiftcommathree.com/articles/how-to-install-mongodb-on-os-x