Ruby On Rails-2.0.2源代码分析（3）-resource

• RESTful的化身----resource

当然，光把RESTful和resource扯到一起似乎相当狭义，在Rails中，ActionController::Resources抽象了REST中的Resource，这里，我不谈REST的相关概念，网上资料一大坨。我们就来看看Rails中是如何通过Resource来轻松，简便的完成RESTful应用的吧。

resources.rb

源代码路径：/actionpack-2.0.2/lib/action_controller/resources.rb
首先，我们也不需要将resource看得多么的高深，你可以把他理解为，当你在routes.rb中定义如下的resource的时候：

map.resources :products
Rails会自动为我们生成众多的named route，这些route通过http verb和相应的controller中的action对应起来，当然了，众多的helper方法也随即产生。如下表所示：

Named Route	Helpers
product	product_url, hash_for_product_url, product_path, hash_for_product_path
new_product	new_product_url, hash_for_new_product_url, new_product_path, hash_for_new_product_path
edit_product	edit_product_url, hash_for_edit_product_url, edit_product_path, hash_for_edit_product_path
...	...

从这个角度来想，你可以把resource想成是众多相关named route的一个马甲。

整个流程比较的直观，Rails通过resource按部就班的完成各种route的生成，接下来我们看一看核心代码是如何完成这些功能的。首先，还是在routes.rb中，可能会定义如下的resource：

ActionController::Routing::Routes.drawdo|map|

map.resources:products
...
end

ActionController::Routing::Routes.draw do |map|

  map.resources :products
  ...
end

resources方法定义在ActionController::Resources这个module中，然后通过mixin进入到Mapper类的。那我们首先来看一看这个方法：

defresources(*entities,&block)
options=entities.extract_options!
entities.each{|entity|map_resource(entity,options.dup,&block)}
end

def resources(*entities, &block)
  options = entities.extract_options!
  entities.each { |entity| map_resource(entity, options.dup, &block) }
end

很简单，将entities和options从参数中分离开来，然后针对每一个entity执行map_resource操作。我们继续进行，看看map_resource方法的真面目：

defmap_resource(entities,options={},&block)
resource=Resource.new(entities,options)

with_options:controller=>resource.controllerdo|map|
map_collection_actions(map,resource)
map_default_collection_actions(map,resource)
map_new_actions(map,resource)
map_member_actions(map,resource)

map_associations(resource,options)

ifblock_given?
with_options(:path_prefix=>resource.nesting_path_prefix,:name_prefix=>resource.nesting_name_prefix,:namespace=>options[:namespace],&block)
end
end
end

def map_resource(entities, options = {}, &block)
  resource = Resource.new(entities, options)

  with_options :controller => resource.controller do |map|
    map_collection_actions(map, resource)
    map_default_collection_actions(map, resource)
    map_new_actions(map, resource)
    map_member_actions(map, resource)

    map_associations(resource, options)

    if block_given?
      with_options(:path_prefix => resource.nesting_path_prefix, :name_prefix => resource.nesting_name_prefix, :namespace => options[:namespace], &block)
    end
  end
end

有了entity和options，还等什么呢？马上生成我们的Resource对象，Resource对象封装了和此resource相关的collection method，member method，new method，path prefix，name prefix，单/复数表示，还有option。生成这个Resource对象无非就是将此对象的相应属性从options中解析出来，保存起来，代码比较简单，这里就不再贴出。
现在，Resource对象有了，从上面代码我们就可以看出来，接下来，就该处理和此resource相关named route了。具体的处理逻辑都类似，这里将map_member_actions(map, resource)拿出来作为示意，感兴趣的同学们可以自己查看相关的源代码。

defmap_member_actions(map,resource)
resource.member_methods.eachdo|method,actions|
actions.eachdo|action|
action_options=action_options_for(action,resource,method)
map.named_route("#{action}_#{resource.name_prefix}#{resource.singular}","#{resource.member_path}#{resource.action_separator}#{action}",action_options)
map.named_route("formatted_#{action}_#{resource.name_prefix}#{resource.singular}","#{resource.member_path}#{resource.action_separator}#{action}.:format",action_options)
end
end

show_action_options=action_options_for("show",resource)
map.named_route("#{resource.name_prefix}#{resource.singular}",resource.member_path,show_action_options)
map.named_route("formatted_#{resource.name_prefix}#{resource.singular}","#{resource.member_path}.:format",show_action_options)

update_action_options=action_options_for("update",resource)
map.connect(resource.member_path,update_action_options)
map.connect("#{resource.member_path}.:format",update_action_options)

destroy_action_options=action_options_for("destroy",resource)
map.connect(resource.member_path,destroy_action_options)
map.connect("#{resource.member_path}.:format",destroy_action_options)
end

def map_member_actions(map, resource)
  resource.member_methods.each do |method, actions|
    actions.each do |action|
      action_options = action_options_for(action, resource, method)
      map.named_route("#{action}_#{resource.name_prefix}#{resource.singular}", "#{resource.member_path}#{resource.action_separator}#{action}", action_options)
      map.named_route("formatted_#{action}_#{resource.name_prefix}#{resource.singular}", "#{resource.member_path}#{resource.action_separator}#{action}.:format",action_options)
    end
  end

  show_action_options = action_options_for("show", resource)
  map.named_route("#{resource.name_prefix}#{resource.singular}", resource.member_path, show_action_options)
  map.named_route("formatted_#{resource.name_prefix}#{resource.singular}", "#{resource.member_path}.:format", show_action_options)

  update_action_options = action_options_for("update", resource)
  map.connect(resource.member_path, update_action_options)
  map.connect("#{resource.member_path}.:format", update_action_options)

  destroy_action_options = action_options_for("destroy", resource)
  map.connect(resource.member_path, destroy_action_options)
  map.connect("#{resource.member_path}.:format", destroy_action_options)
end

这里，我们可以很直观的看到，Rails为resource的member相关方法生成了众多的route，我们可以看到Controller中熟悉的show，update，destroy action。是的，在这里，Rails就为url到controller的action生成了相应的route。

本文转自:http://woody-420420.javaeye.com/blog/174352