Rake简介及如何自定义Rake任务（rake task） - 好文

Rake是基于ruby语言的项目中用于自动化字形任务的一个友好又非常强大的工具

基于我们使用rake的目的，让我们来看一些简单的例子：

安装Rake
# 在Gemfile中添加rake gem 'rake', '~> 10.4.2' # 执行安装 bundle install
Rake语法

Rake任务约定如下：
desc '...' task :name do # task code ... end
如上图所示，'desc', 'name'和‘code’是主要的三个部分。虽然该脚本是ruby写的，但是文件后缀要为.rake而非.rb。

列出所有的Rake任务

列出所有可用的任务：
$ bundle exec rake -T
列出所有可用的任务以及其desc：
$ bundle exec rake -vT

小试牛刀：

定义个hello的任务去输出"Hello"
[wlin@localhost tasks]$ cat hello_world.rake desc 'This is my first rake task
to say "hello"!' task :hello do puts "Hello" end [wlin@localhost tasks]$ bundle
exec rake hello (in /home/wlin/ROR_Blog) Hello [wlin@localhost tasks]$ pwd
/home/wlin/ROR_Blog/lib/tasks [wlin@localhost tasks]$

创建负责一些的rake任务

其实，rake就是可执行的ruby脚本。所以，rake可以做所以可以用ruby脚本能做的事情。

现在我们让这个task去找到所有的models并为其创建CSV文件。这些CSV文件可以用来初始化数据库。
[wlin@localhost tasks]$ cat create_csv_files_for_models.rake namespace :db do
namespace :seed do desc "Create CSV Files for Models" task :create_files =>
:environment do Dir.glob("#{Rails.root}/app/models/*.rb").each { |file| require
file } dir = "#{Rails.root}/db/csv" FileUtils.mkdir(dir) unless
Dir.exists?(dir) ActiveRecord::Base.descendants.each do |model| unless
File.exists?("#{dir}/#{model.to_s.tableize}.csv") csv_dir =
File.dirname("#{dir}/#{model.to_s.tableize}.csv") FileUtils.mkdir(csv_dir)
unless Dir.exists?(csv_dir) File.open("#{dir}/#{model.to_s.tableize}.csv",
'w+') do |f| f.write(model.columns.collect(&:name).join(',')) end puts "CREATED
FILE >> #{model.to_s.tableize}.csv" end end end end end [wlin@localhost tasks]$
bundle exec rake -T db (in /home/wlin/ROR_Blog) rake db:create # Creates the
database from DATABASE_URL or config/database.yml for the current RAILS_ENV
(use db:create:all to create all databases in the config). Without RAILS_ENV it
defaults... rake db:drop # Drops the database from DATABASE_URL or
config/database.yml for the current RAILS_ENV (use db:drop:all to drop all
databases in the config). Without RAILS_ENV it defaults to dr... rake
db:fixtures:load # Load fixtures into the current environment's database rake
db:migrate # Migrate the database (options: VERSION=x, VERBOSE=false,
SCOPE=blog) rake db:migrate:status # Display status of migrations rake
db:rollback # Rolls the schema back to the previous version (specify steps w/
STEP=n) rake db:schema:cache:clear # Clear a db/schema_cache.dump file rake
db:schema:cache:dump # Create a db/schema_cache.dump file rake db:schema:dump #
Create a db/schema.rb file that is portable against any DB supported by AR rake
db:schema:load # Load a schema.rb file into the database rake db:seed # Load
the seed data from db/seeds.rb rake db:seed:create_files # Create CSV Files for
Models rake db:setup # Create the database, load the schema, and initialize
with the seed data (use db:reset to also drop the database first) rake
db:structure:dump # Dump the database structure to db/structure.sql rake
db:structure:load # Recreate the databases from the structure.sql file rake
db:version # Retrieves the current schema version number rake test:all:db # Run
tests quickly, but also reset db rake test:db # Run tests quickly, but also
reset db [wlin@localhost tasks]$ bundle exec rake db:seed:create_file (in
/home/wlin/ROR_Blog) CREATED FILE >> delayed/backend/active_record/jobs.csv
CREATED FILE >> categories.csv CREATED FILE >> posts.csv CREATED FILE >>
users.csv
其中，

* 'namespace'是用来对'rake'任务进行分组。在我们的代码中有两个‘namespace’，则对应的rake任务为“rake
namespace1:namespace2:task_name”即'db:seed:create_file'
* ’=> :environment ‘不能省略。该代码用来加载当前环境，使得我们可以访问'ActiveRecord'模块
* ‘glob’找到指定路径中的满足格式的所有文件，并返回一个列表
*
‘ActiveRecord::Base.descendants’是指“ActiveRecord::Base”的所有子类，而我们定义的所有model都是“ActiveRecord::Base”的子类。

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