Here are some of the problems i faced and the solutions to those ..

Firstly,

How  to write a plugin ?

Its quite easy. There are many tutorials over the web tha will give you a nice guidelines on it.

I shall just put it up for you.

Creating the plugin

First, generate the basic code for a plugin:

./script/generate plugin <YOUR_PLUGIN_NAME>

This will create a new directory in vendor/plugins containing all the basic files you need.

The vendor/plugins/acts_as_exportable/lib/<YOUR_PLUGIN_NAME>.rb contains a module that’s named after our plugin:

module YOUR_PLUGIN_NAME
end

Next, we add a module named ‘ClassMethods’.
These class methods will be added to ActionController::Base when the plugin is loaded.
For more info
http://ariejan.net/2007/07/06/how-to-write-a-rails-plugin-for-controllers/

Enabling the plugin by default

We have a very nice plugin now, but it is not loaded by default! If you take a look at your plugin directory,
in this create a directory, rails and a initiliser file init.rb
Similiar to the rails application. The loader searches for the “rails/init.rb” in your plugin.

--rails
 |--- init.rb

--plugin
 |--lib
 |--rails
    |--init.rb

And thats it.
Now, Secondly
How to add Controllers, Helpers, and Models to your Plugin?
Its very easy
in the file: “rails/init.rb” in vendor/plugins/YOUR_PLUGIN
Copy your controllers, models, helpers, views in a directory under vendor/plugins/YOUR_PLUGIN/lib/app

similar to the rails application.

app/controllers

app/helpers

app/views

app/models

And then just add the following lines in the file: “rails/init.rb” in vendor/plugins/YOUR_PLUGIN

%w{ models controllers helpers }.each do |dir|

path = File.join(directory, ‘lib/app’, dir)

$LOAD_PATH << path

#The Dependencies class has now changed to ActiveSupport::Dependencies

ActiveSupport::Dependencies.load_paths << path

ActiveSupport::Dependencies.load_once_paths.delete(path)

end

Thats it. All the controllers, helpers, Models will be loaded in the main app when the server starts.

Thirdly, one more issue you fill face is :
How to add the views to your Plugin?
Thats to simple from now..
Just copy the below line in the rails/init.rb

ActionController::Base.append_view_path(File.join(directory, “lib/app”, “views”))

and you are done. All your views for the plugin shall be included in the main application.

Hope this helps you in your plugins ..

Good Luck

Hansraj

Some more issues you might come through, are

1.   Can’t dup NilClass error

The can’t dup NilClass error was really tricking  me.

It seemed to be saying something about duping nil class but not really.  The problem is that your app tries to re-load

the plugin models / controllers in the ‘development ‘ environment.

But as it already has it loaded, it gives this error. Hence it must be taken care of.

On many of the post and blogs around, you will find that using “unloadable” in the app solves the problem.

But, as i know, it has been depricated.

Thats no the part to worry..

To get over this error, we have 2 options :

Firstly, while exporting your plugins path to the app, you need to add the following to the init.rb of your plugin.

load_paths.each do |path|
ActiveSupport::Dependencies.load_once_paths.delete(path)
end if config.environment == ‘development’

and thats it..

The second approach has two steps.

First, you could put something like this in your plugin’s init.rb file:
# This plugin should be reloaded in development mode.
if RAILS_ENV == ‘development’
ActiveSupport::Dependencies.load_once_paths.reject!{|x| x =~ /^#{Regexp.escape(File.dirname(__FILE__))}/}
end

Second, you could put something like this in your application’s environment.rb file:
config.reload_plugins = true if RAILS_ENV == ‘development’

And you are done.