Whenever you start a process to handle requests with Rails (such as a Webrick server), one of the first things that happens is that config/environment.rb is loaded. For instance, take a look at the top of public/dispatch.rb:
require File.dirname(__FILE__) + “/../config/environment”
A word of caution: If you were to set the RAILS_ENV environment variable to production here, or the constant variable RAILS_ENV for that matter, it would cause everything you did in Rails to run in production mode. For instance, your test suite would not work correctly, since test_helper.rb sets RAILS_ENV to test right before loading the environment.
因为在test/test_helper.rb中，先是：
ENV["RAILS_ENV"] = "test"
再是：
require File.expand_path(File.dirname(__FILE__) + "/../config/environment")
而在加载environment.rb时，又将RAILS_ENV覆写为prodoction。
项目中使用的Rails的版本：
RAILS_GEM_VERSION = '2.0.1' unless defined? RAILS_GEM_VERSION
定义项目根目录：
RAILS_ROOT = "#{File.dirname(__FILE__)}/.." unless defined?(RAILS_ROOT)
RAILS_ROOT is used all over the place in the Rails codebase for finding files
read the config/environment.rb file as text (minus the commented lines) and parse out the RAILS_GEM_VERSION setting with a regexp.
parse_gem_version(read_environment_rb)
def parse_gem_version(text)
$1 if text =~ /^[^#]*RAILS_GEM_VERSION\s*=\s*'([!~<>=]*\s*[\d.]+)'/
end
def read_environment_rb
File.read("#{RAILS_ROOT}/config/environment.rb")
end
Default Load Paths:
def default_frameworks
[ :active_record, :action_controller, :action_view, :action_mailer, :active_resource ]
end
def default_load_paths
paths = ["#{root_path}/test/mocks/#{environment}"]
paths.concat(Dir["#{root_path}/app/controllers/"])
paths.concat(Dir["#{root_path}/components/[_a-z]*"])
paths.concat %w(
app
app/models
app/controllers
app/helpers
app/services
components
config
lib
vendor
).map { |dir| "#{root_path}/#{dir}" }.select { |dir| File.directory?(dir) }
paths.concat builtin_directories
end
def builtin_directories
(environment == 'development') ? Dir["#{RAILTIES_PATH}/builtin/*/"] : []
end
def default_plugin_paths
["#{root_path}/vendor/plugins"]
end
上面这个builtin_directories指的是：
It is the place for Rails to include application behavior (meaning models, helpers, and controllers). You can think about it as kind of like a framework-provided plugin mechanism.
http://localhost:3000/rails/info/properties
和在命令行下用script/about是一样的
在Rails项目里，绝大多数情况下，都不需要手动去load一个class或module，Rails有默认的规则去自动load需要的文件，其规则如下：
• If the class or module is not nested, insert an underscore between the constant’s names and require a file of this name. For example:
EstimationCalculator becomes require ‘estimation_calculator’
• If the class or module is nested, Rails inserts an underscore between each of the containing modules and requires a file in the corresponding set of subdirectories.For example:
MacGyver::SwissArmyKnife becomes require ‘mac_gyver/swiss_army_knife’
you should rarely need to explicitly load Ruby code in your Rails applications (using require) if you follow the naming conventions.
哈哈，顺我者昌
Rails::Initializer.run do |config|
...
end
里面的代码是关于Configuration的
The comment reminds you that the settings in the mode-specific environment files will take precedence over settings in environment.rb, which is essentially because they are loaded afterward and will overwrite your settings.
如果项目中不用数据库，就去掉Active Record，如果不用Web service或Email，也去掉相应的模块
为什么要去掉呢：
Ruby is, of course, interpreted, and if you can get away with a smallersized codebase for the interpreter to parse, you should do so, simply for performance reasons.
plugins默认是按照字母顺序load的，也可以指定先load哪些plugin，再load剩下的(:all)
Rails takes advantage of the fact that Ruby provides a callback mechanism for missing constants. When Rails encounters an undefined constant in the code, it uses a classloader routine based on file-naming conventions to find and require the needed Ruby script.
利用Ruby提供的"missing constants"回调机制，Rails根据命名惯例去找对应的文件来load。
Want to see the contents of your project’s load path? Just fire up the console and type $:
想看项目里的load path的话，就script/console，然后敲$:（注意加上后面的冒号），然后load path就打出来了，一长串。$:是一个数组。
除了Rails提供的三种environment外，还可以自定义environment，比如：
Use the normal environment settings for development mode, but point its database connection to a production database server. It’s a potentially life-saving combination when you need to quickly diagnose issues in production.
可以用来快速诊断生产环境的问题。
使用log的方法：在irb里敲入：
require ‘logger’
logger = Logger.new STDOUT
logger.warn “do not want!!!”
log的级别（按严重程度由低到高）：
debug -> info -> warn -> error -> fatal
debug是开发时方便调试程序的，生产环境中用不到。
info是一些不常发生的事件，但仍然属于正常行为范围内。
warn表示正常范畴之外的事件发生了，需要注意，值得去研究研究问题，例如：
def create
begin
@group.add_member(current_user)
flash[:notice] = “Successfully joined
rescue ActiveRecord::RecordInvalid
flash[:error] = “You are already a member of
logger.warn “A user tried to join a group twice. UI should not have allowed it.”
end
redirect_to :back
end
error表示还不需要重启服务器的错误。
fatal是指能想到的最坏的情况已经发生了，你的应用现在已经挂了，需要重启服务器了。
清空log/目录下的所有.log文件
rake log:clear
development.log里包含的信息：
• The controller and action that were invoked
• The remote IP address of the computer making the request
• A timestamp indicating when the request happened
• The session ID associated with the request
• The hash of parameters associated with the request
• Database request information including the time and the SQL statement executed
• Query cache hit info including time and the SQL statement triggering results from the cache instead of a roundtrip to the database
• Rendering information for each template involved in rendering the view output and time consumed by each
• Total time used in completing the request with corresponding request-per-second figures
• Analysis of the time spent in database operations versus rendering
• The HTTP status code and URL of the response sent back to the client
资源/链接：
Rails Plugins: Extending Rails Beyond the Core
http://weblog.jamisbuck.org/2007/1/31/more-on-watchingactiverecordhttp://seattlerb.rubyforge.org/SyslogLogger/
