reuse your project with rails engine part 1

_posts/2013-12-26-reuse-your-project-with-rails-engine-1.markdown

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+---
+layout: post
+title:  "Reuse your project with rails engine - part 1"
+date:   2013-12-26 17:28:00
+categories: rails, rails engine
+---
+
+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