Reuse your project with rails engine - part 1

这片文章的核心是在同类项目中快速重用一个小型的项目文件，包括view，controller，model等等，同时也可以很容易的去重载它们。在part 2中，我会尝试提供一种helper的重用机制，另外会描述删除engine的namspace，也就是说不再使用Hr::。

How to create a Namespace Less Engine

Imagine that we have HR system that could be reused in different companies' projects.

$ rails plugin new hr --full
$ rails g resource hr/department name
$ rails g resource hr/employee first_name last_name department:references
$ rake db:migrate

Comment out the table_name_prefix in /app/models/hr.rb. Because I don't want my table names to end up being like hr_departments, hr_employees.

module Hr
  def self.table_name_prefix
    # 'hr_'
  end
end

Do the same things for routes, so that the urls aren't scoped under /hr.

Rails.application.routes.draw do
  resources :employees
  resources :departments
end

Add placeholder models & controllers, so that we could write code without Namespace. And this also makes sure that we could define a Department, which inherits Hr::Department in our project, to override the default behavior.

class DepartmentsController < Hr::DepartmentsController
end

class EmployeesController < Hr::EmployeesController
end

class Department < Hr::Department
end

class Employee < Hr::Employee
end

Add a default behavior to Department

class Hr::Employee < ActiveRecord::Base
  def full_name
    [first_name, last_name].join(" ")
  end
end

To test the Engine in the Dummy project.

$ cd test/dummy/
$ rails s

Reuse Hr Engine for Kude company

Create a new project, Kude:

$ rails new kude

In the Gemfile of Kude:

gem 'hr', :path => "../hr"
# change to the path to the hr engine
bundle
# to install the engine

$ rake hr_engine:install:migrations
$ rake db:migrate
$ rails s

An example to override the Hr::Employee, to make the full_name return in Chinese style. Note that you should define this in your project.

class Employee < Hr::Employee
  def full_name
    [last_name, first_name].join("")
  end
end

# test it out
rails c
Hr::Employee.new(first_name: "少坤", last_name: "伍").full_name
=>
少坤 伍

Employee.new(first_name: "少坤", last_name: "伍").full_name
=>
伍少坤