# Some questions **URL:** \ **Category:** Engines\ **Created:** [September 3, 2008, 5:26am UTC](https://www.ruby-forum.com/t/some-questions/147559 "2008-09-03T05:26:13Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Chris\_Griffin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/7cd45c/32.png) [@Chris\_Griffin](https://www.ruby-forum.com/u/Chris_Griffin)\ **Post date:** [September 3, 2008, 5:26am UTC](https://www.ruby-forum.com/t/some-questions/147559/1 "2008-09-03T05:26:13Z")
First of all the two links to articles on building plugins to take advantage for engines are broken. a guide building plugins that can take advantage of the engines plugin’s features best introductions to developing an engine My first question is how do you handle a plugin that has a controller with the same name a your current rails app does? Second, how do you handle the database? Do you have two separate DBs? If so how does that work? Or is there code in the engines plugin to handle multiple DBs? I’m interested in developing some plugins for engines so if there is more information you can point me to that would be great. Best regards, Chris Griffin removed\_email\_address@domain.invalid ---
**Author:** ![Chris\_Griffin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/7cd45c/32.png) [@Chris\_Griffin](https://www.ruby-forum.com/u/Chris_Griffin)\ **Post date:** [September 3, 2008, 5:54am UTC](https://www.ruby-forum.com/t/some-questions/147559/2 "2008-09-03T05:54:16Z")
In Ruby, redefining a class simply adds/overwrites the original class. So, if you had an ApplicationController in your main app, and installed an engine plugin with a controller of the same name, the methods defined in the second class would add to the application’s core controller class. However, I think you’re asking about routing, namely, if I have a WidgetsController with a method index in my main app, and a WidgetsController that _also_ has an index method, which wins? Good question. 🙂 My bet would be that the view defined in the main app would win in a race, due to the search order for finding views. The index method itself would be the plugin’s definition, as the plugin’s WidgetsController class would be loaded second, and thus overwrite the main apps definition. Bad juju. In practice, you should aim for some name scoping for your controllers. This generally happens naturally (ie, if you have an engine that provides user management, why would you have a UsersController in your main app?). I _think_ Rails has some facility for using namespacing in controllers and routes as well, but I haven’t used it, so can’t help much there. As for databases, the database is shared by default. You build migrations to add whatever tables your engine needs. You can, of course, use the normal Rails database segmentation stuff to point your models to a second database, but I don’t think that’s very common. It would require a lot of front-end work to install the plugin, which is counter to the plugin way. Really, engine plugins are best used internally (IMHO). I’ve used them to build application verticals that I can reuse for multiple consulting clients. Drop in the wiki engine, and now the site has wikis. As such, I don’t have collisions with naming/tables/routing. The engines are core application resources that I install before the site is designed. If I need to customize a certain view or whatever, I usually do it by grabbing the request out via my app’s routes.rb file, and pointing it to /site/wiki\_view or whatever, instead of /wikis/view. Hope that helps. Perhaps someone who has done more work with making “generic” plugins based on engines could speak more to the deconflicting issues. -Rob ---
**Author:** ![Chris\_Griffin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/7cd45c/32.png) [@Chris\_Griffin](https://www.ruby-forum.com/u/Chris_Griffin)\ **Post date:** [September 3, 2008, 6:58am UTC](https://www.ruby-forum.com/t/some-questions/147559/3 "2008-09-03T06:58:00Z")
I kinda had in mind 2 different situations when I asked my questions. The first situation was a particular engines plugin substruct. The second situation you mentioned, building application verticals. The second is really the one I’m most interested in as I believe it could make for building sites more quickly. Thanks for your detailed response. Best regards, Chris Griffin removed\_email\_address@domain.invalid On Sep 2, 2008, at 8:53 PM, Rob M. wrote: In Ruby, redefining a class simply adds/overwrites the original class. So, if you had an ApplicationController in your main app, and installed an engine plugin with a controller of the same name, the methods defined in the second class would add to the application’s core controller class. However, I think you’re asking about routing, namely, if I have a WidgetsController with a method index in my main app, and a WidgetsController that _also_ has an index method, which wins? Good question. 🙂 My bet would be that the view defined in the main app would win in a race, due to the search order for finding views. The index method itself would be the plugin’s definition, as the plugin’s WidgetsController class would be loaded second, and thus overwrite the main apps definition. Bad juju. In practice, you should aim for some name scoping for your controllers. This generally happens naturally (ie, if you have an engine that provides user management, why would you have a UsersController in your main app?). I _think_ Rails has some facility for using namespacing in controllers and routes as well, but I haven’t used it, so can’t help much there. As for databases, the database is shared by default. You build migrations to add whatever tables your engine needs. You can, of course, use the normal Rails database segmentation stuff to point your models to a second database, but I don’t think that’s very common. It would require a lot of front-end work to install the plugin, which is counter to the plugin way. Really, engine plugins are best used internally (IMHO). I’ve used them to build application verticals that I can reuse for multiple consulting clients. Drop in the wiki engine, and now the site has wikis. As such, I don’t have collisions with naming/tables/routing. The engines are core application resources that I install before the site is designed. If I need to customize a certain view or whatever, I usually do it by grabbing the request out via my app’s routes.rb file, and pointing it to /site/wiki\_view or whatever, instead of / wikis/view. Hope that helps. Perhaps someone who has done more work with making “generic” plugins based on engines could speak more to the deconflicting issues. -Rob