What is the difference between the two and when one should be used instead of the other?
An Engine in rails terminology is a actually a subapplication of a web-application. For instance, something like a blog, a forum, or simple authentication: these are not full-blown applications, but pages/views/controllers/models that can be added to any rails application.
In rails2 this would be done using a plugin. Now since rails3 an engine can be packaged in a gem.
A gem is a ruby library, which can be found on http://rubygems.org and it is the standard (only) way to package and distribute ruby code to other rubyists.
So to conclude:
A gem: is a generic library, which can be easily installed, which are version-managed, have dependencies and such.
An engine: is a sub-application of a Rails application, and since Rails 3 these are distributed as a gem (which is awesome!).
So when will you use one or the other:
create a gem if you want to share ruby-functionality
create an engine (and package it in a gem) if you have parts of your rails application that can be used more generally.
Hope this helps.
Related
can anyone help me how to create a web service API in rails 4. I know how create web service API in ruby 1.8.7 and rails 2.3.5 with action web service gem. When I am trying to use https://github.com/datanoise/actionwebservice gem in rails 4, I am getting deprecated errors.I want to upgrade my web service app. Please help me.
Rails-API looks promising, because it will be part of Rails core in Rails 5.
Rails-API
Rails-API is a subset of a normal Rails application, because API only applications don't require all functionality that a complete Rails application provides. so, it compatible well with old Rails versions. I don't know compatibility exactly, but I'm using it with Rails 3.2.x
There are another proper framework for this purpose, for example, Sinatra, Grape, but If you familiar with Rails, Rails-API will be the best choice.
Actionwebservice is long deprecated, in favour of REST API's. At my previous job we used a fork of actionwebservice in a rails 3 project.
Since there is no maintainer anymore for the actionwebservice gem, that fork never got merged back. If you check the fork history, a lot of people are fixing and partially updating it, but it is scattered all over the place.
Afaik none of the forks were updated to use rails 4. But using a rails 3 fork might just work.
If you really need to build a SOAP API server with Rails, imho your best option is to take a look at Wash-out, but you will have to re-write your API code.
I want to create a sms payment engine and reuse it in several applications. It would be best to be able to just copy/paste one directory, maybe configure some minor stuff and just have it working (with views, controllers, etc.).
What's the best way to do this? Of course I'm not asking about this sms thing but about the way to create an isolated piece of application. It's something like a helper application inside of the major application.
There a three ways to build Rails extensions : plain-old ruby code, Railties and Engines.
Railties and Engines allow you to interact with the Rails framework during the initialization using hooks and therefore extend Rails. Actually, every major Rails component (ActiveRecord, ActionPack, etc.) is a Railtie.
The main difference between a railtie and a Rails engine is that an engine can define its own configuration, models, controllers and views. In a way, an engine is a Rails application you can deploy in another one. In your case, I guess a Rails Engine would be the right choice.
Whatever the option you use, you will have to build a gem to distribute your extension and share it across projects.
Here is a gist explaining both the Railtie and Engine concepts
A guide to starting your own rails engine.
Enginex, a command line tool which creates a Rails 3 Engine
I guess the best way to reuse your code is putting them to a gem, then install that gem.
I think the best way to extract reusable part of your application is to create a RubyGem. You can find a tutorial about creating RubyGems here. And there is a Jeweler, a very nice tool to create RubyGems. More about Jeweler, you can find here
I am writing a gem that requires rails as a dependency (for using Rails methods like underscore, camelize and others).
Is 'gem' still a gem or is it now something else (Rails Plugin?) since I have rails as a dependency?
You don't have to depend on Rails as a whole (in fact if it really is a standalone gem, I would recommend that you do not) you can depend on just the parts of it that provide the functionality you need, in this case you are talking about ActiveSupport.
As a Rails developer I feel a bit stupid asking this question but hopefully I will learn something new and someone can put me out of my misery! In my rails applications I use (other peoples) gems all the time, I also use plugins from the community or my own.
I understand the benefits of use gems over plugins as they are version-able, segmented, system wide, easier to manage and share etc etc but I don't really know how to go about making a gem for my rails apps!?
Do you always start with a plugin and convert it to a gem, I've seen the words 'package it as Gem'. Also the gem I'm thinking of building would be no good in a normal ruby program, it's only useful to rails apps. I'm not even sure if the semantics of that make sense, 'RubyGem' that will only work in a rails application!?
I would like to create a gem (if that's what I should use?) for a discrete piece of functionality for my rails apps. It will need to add a database migration, new routes and provide controllers and views or useful view helpers. I'm know I can achieve this via a plug-in but would just like to know how/why to do it as a 'Ruby Gem'?
To avoid the risk of Over-engineering, I usually start with the feature I need directly into the application. Then, as soon as I need to use the same feature into another project, I check whether it is worth to extract it into a plugin or even a separate application providing an API.
Plugins and Gems are often interchangeable. Gems provides several significant advantages in terms of reusability and maintainability.
On the other side, there are some specific known issue. For instance, a Rails app actually can't load rake tasks defined into a plugin packaged as a Gem.
Almost every Rails plugin can be packaged as a Gem.
For instance, take my tabs_on_rails plugin.
You can install it as a Gem specifying the dependency on environment.rb. Or you can use script/plugin install command as you would expect.
If you want to achieve the same result, make sure to follow the standard Gem layout and provide the init.rb initialization script required by Rails.
Also, you might want to create an install.rb and uninstall.rb file to include the post-install and post-uninstall hooks when the plugin is installed as a standard Rails plugin.
Last but not least, if you package a plugin as Gem you can reuse it in non-Rails projects and provide Rails-specific initializations using the init.rb file. Non-Rails applications will simply ignore it.
If you want to make a plugin for Rails, https://peepcode.com/products/rails-2-plugin-patterns gives you a good start. After that, make the plugin into a gem.
To make a gem, this resource http://railscasts.com/episodes/183-gemcutter-jeweler will be helpful.
As of 2013 you'll want to use Bundler and the following tutorials:
#245 New Gem with Bundler -
RailsCasts
Make your own gem - RubyGems
Guides
Take a look at Jeweler. Jeweler gives you a set of rake tasks to make gem versioning and building very easy.
I have developed a simple library in Ruby and need to use this in several Rails applications (some of which are not built yet). What is the best way to easily add this Ruby library to several Rails applications as and when required? Our team is running Ubuntu and our repository is Mercurial.
Should I use a...
Rails plugin? This would be my first
choice but it appears not to support
Mercurial??
Ruby Gem?
Custom Rake script?
Other options??
Any pointers would be much appreciated!
Ruby already has an established mechanism for code sharing i.e. RubyGems. Jeweler makes Gem creation easy. I'd recommend that you check it out.
Make a gem or a plugin. Gems are better in my opinion, easier to manage.
My rule of thumb:
If it doesn't depend on rails, make it a gem.
If it depends on rails, make it a plugin.
Make a Rails plugin. It doesn't "support" Mercurial in the sense that you can't do script/plugin install $REPO_URL and have it work automatically, but if it's for your own use, then you won't miss that feature.