如何写gem

第一步：用bundle gem gem_name生成基本结构，如下：

[root@arch demo]$ bundle gem rename_url
      create  rename_url/Gemfile
      create  rename_url/Rakefile
      create  rename_url/.gitignore
      create  rename_url/rename_url.gemspec
      create  rename_url/lib/rename_url.rb
      create  rename_url/lib/rename_url/version.rb
Initializating git repo in /home/suchj/programs/demo/rename_url

注：

Gemfile # 描述依赖

Rakefile # 发布和打包的 rake tasks

GEM_NAME.gemspec # gem 的 spec

GEM_NAME/lib/GEM_NAME.rb 与 GEM_NAME/lib/GEMNAME/ # gem 里的 library

GEM_NAME/lib/GEM_NAME/version.rb # 版本记录

第二步：写Gems规范文件，rename_url.gemspec

# -*- encoding: utf-8 -*-
$:.push File.expand_path("../lib", __FILE__)
require "rename_url/version"

Gem::Specification.new do |s|
  s.name        = "rename_url"
  s.version     = RenameUrl::VERSION
  s.authors     = ["xx"]
  s.email       = ["[email protected]"]
  s.homepage    = ""
  s.summary     = %q{TODO: Write a gem summary}
  s.description = %q{TODO: Write a gem description}

  s.rubyforge_project = "rename_url"

  s.files         = `git ls-files`.split("\n")
  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
  s.require_paths = ["lib"]

  # specify any dependencies here; for example:
  # s.add_development_dependency "rspec"
  # s.add_runtime_dependency "rest-client"
end

 

第三步：写实现，lib/rename_url.rb

require "rename_url/version"

module RenameUrl
  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def urlize
      include RenameUrl::InstanceMethods
    end
  end

  module InstanceMethods
    def to_param
      "#{id}_#{title}"
    end
  end
end

ActiveRecord::Base.send(:include, RenameUrl) #在model中引入

 第四步：打包gem

[root@arch rename_url]$ gem build rename_url.gemspec 
WARNING:  no homepage specified
  Successfully built RubyGem
  Name: rename_url
  Version: 0.0.1
  File: rename_url-0.0.1.gem

 注：如果规范文件有信息没写全，会有警告

第五步：使用，在项目的Gemfile中加入

gem 'rename_url', :path => '~/programs/rename_url'

 注：gem文件在哪就写哪个路径

post.rb

class Post < ActiveRecord::Base
  urlize #相当于include RenameUrl::InstanceMethods
end

测试：

[root@arch demo]$ rails c
Loading development environment (Rails 3.0.4)
1.8.7 :001 > Post
 => Post(id: integer, name: string, title: string, content: text, created_at: datetime, updated_at: datetime) 
1.8.7 :002 > Post.create(:title => "test")
 => #<Post id: 2, name: nil, title: "test", content: nil, created_at: "2012-02-03 08:38:53", updated_at: "2012-02-03 08:38:53"> 
1.8.7 :003 > Post.find_by_title("test").to_param
 => "2_test" 

 OK，一个简单的gem就完成了。

当然，一个完整的gem有完整的测试，还可能会放到git和rubygems上供大家使用，此例子纯粹供练手，仅供参考。