# Components vs engines **URL:** \ **Category:** Rails\ **Created:** [November 25, 2005, 2:55am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804 "2005-11-25T02:55:40Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 25, 2005, 2:55am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/1 "2005-11-25T02:55:40Z")
Hi, What are the main differences between components vs. engines? It looks like the are both vertical slices of an application. Thanks, Peter ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 25, 2005, 9:30am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/2 "2005-11-25T09:30:16Z")
[http://rails-engines.rubyforge.org/wiki/wiki.pl?ComponentsPluginsEngines](http://rails-engines.rubyforge.org/wiki/wiki.pl?ComponentsPluginsEngines) Components are essentially like partials with their own controller logic - meant to be rendered within other views. Engines can have full-blown views, controllers, helpers, possibly models, libraries… all or only as much of that list as you need. - james ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 25, 2005, 4:30pm UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/3 "2005-11-25T16:30:51Z")
Peter M. wrote: > What are the main differences between components vs. engines? It looks > like the are both vertical slices of an application. Components are less feature blessed, but fit very nicely into the framework. The Engine is opposite of that. –Steve ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 25, 2005, 5:23pm UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/4 "2005-11-25T17:23:38Z")
On 11/25/05, Stephen W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Components are less feature blessed, but fit very nicely into the > framework. The Engine is opposite of that. _sigh_ ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 26, 2005, 5:13am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/5 "2005-11-26T05:13:24Z")
Hi, Reading in the Rails book[1] and looking at the ActiveRBAC component[2] it seems that components have a nasty directory structure. I don’t see any hierarchical logic to the following structure. Lumping models and controllers and then somehow views are contained in this lump. components/ component/ role.rb role\_controller.rb role/ view.rhtml Integrated in a Rails apps these files would be so nicely divided up in the app directory app/ models/ role.rb controllers/ role\_controller.rb view/ view.rhtml Does the seemingly messy directory structure of the component indicate that the components facility is asked to do too much in this case? Could the component’s files structure be improved or does convention make that difficult? Would an engine be a better way to go? Thanks, Peter [1] Agile Web D. with Rails (p376) [2] [https://rbaconrails.turingstudio.com/trac/wiki](https://rbaconrails.turingstudio.com/trac/wiki) ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 30, 2005, 2:16am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/6 "2005-11-30T02:16:13Z")
Back in the days of 0.9, we were looking at cleaning up components to match the app structure. So you’d be able to do things like: components/ component/ controllers/ role\_controller.rb models/ role.rb views/ role/ view.rhtml If I recall, the changes included a few extra default path patterns, a 2-line change in rendering so that one could override component layouts from within the regular app/ tree, and a minor fix to uses\_component\_template\_root. The sticking point was that each component controller would need to include the line ‘uses\_component\_template\_root’ which was the one sticking point I never figured out how to do. If that could be figured out, one could use svn externals to another project’s app/ directory, and have a local copy with no fuss. Alas, I never had the time to finish things, and in the rapid development going forward I gave up on them. > From what I understand though, the reason components is so crappy is > because someone half-thought through the idea, and abandoned it. > Nobody’s backed it out of the framework, and nobody’s stepped up to do > it right either. - Jamie ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 26, 2005, 9:27am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/7 "2005-11-26T09:27:17Z")
> Reading in the Rails book[1] and looking at the ActiveRBAC > component[2] it seems that components have a nasty directory > structure. I don’t see any hierarchical logic to the following > structure. I think you’ve nailed it - I’ve been avoiding components for the same reason. The parts of my app that I’d like to reuse in other projects, I’m planning on building as engines. Hammed ---
**Author:** ![petermichaux](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@petermichaux](https://www.ruby-forum.com/u/petermichaux)\ **Post date:** [November 30, 2005, 3:28am UTC](https://www.ruby-forum.com/t/components-vs-engines/48804/8 "2005-11-30T03:28:45Z")
Interesting points there Jamie. I’ve had a bit of a stab at something similar, but just like you, I haven’t persisted with it due to the need to actually press on with development. I’d really like components to get to a point where (or be replaced by) they are identical from rails apps themselves. This self-similar structure would allow for better re-use of regularly repeated parts of the application which could be tested, and possibly also used, as stand alone apps. And before anyone says it, yes engines are great, but no they don’t do the same thing. Engines give a site an area of functionality (a vertical slice if you will). Components give your site a drag and drop ‘think’ which contains complex functionality but can be ‘instanced’ many times on the site. eg: Engine: I want my site to have blogging functionality, accessed via the blog controller. Component: I want to be able to add editable blogs to pages on my site, accessed via whatever controller manages those pages. regards, Craig