# Large RoR systems design and implementation **URL:** \ **Category:** Rails\ **Created:** [February 4, 2009, 4:00am UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388 "2009-02-04T04:00:33Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 4, 2009, 4:00am UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/1 "2009-02-04T04:00:33Z")
Hi, I’ve implemented a few big RoR apps. I do have some good experience building large systems in many different languages and platforms but I don’t consider myself a RoR guru, so I’d like you experts comment on my thoughts. I’d like to divide a large system (app) into several functional, high- level sub-systems. These are higher level than rails Models, and provide APIs that implement business logic around functional groups. Examples of these are billing manager, security manager (accounts, privileges, roles, etc), inventory manager, manufacturing manager, and such (of course, these are just examples, but you get the point). These high-level sub-systems may be implemented as servers (think SOAP / REST / XML-RPC / …), or just plain Ruby classes. Some of these sub-systems implement integrations with other systems, for example, a credit card gateway, an accounting system, Fedex, you name it. Some of the sub-systems may be just proxies to a system implemented on some other technology. The user interface (views) would not have access to any of the Models. They just present and / or grab data that is prepared for them / pushed back to the controllers as local variables / arrays / hash tables that don’t reflect an actual Model. The controllers do not have access to Models either. Instead, they call methods from the high-level functional sub-system APIs. The Models implement lower-level business logic related to how to the information is stored and retrieved from the database, the pertinent validations, associations, etc. but do not implement high-level business logic such as “how do I bill Joe for a specific event that results in the combination of many other parameters and variables that at the end come from diverse fields on many different tables on the underlying database structure”. The high-level sub-systems all share the same database and therefore same data model and only communicate with each other via their APIs, and can access all Models directly. In other words, this would work more or less as a new layer in between the MVC pattern: view \<-\> controller \<-\> high-level sub-system \<-\> models \<-\> database The idea is to build the app in a more robust / less coupled way where I can exchange parts of the app by different technologies and other applications in the future without having to recode a bunch of things. For example, the security subsystem could one day be replaced by an AAA server and then the subsystem would be re-implemented to call the AAA server (to replace its own original implementation), however the rest of the app would continue to use the same API calls to the security subsystem and so the change is isolated from the rest of the app. The problem with this is, I’d loose many of the RoR goodness, such as form helpers, easy models validation thrown back to the interface, etc. Am I missing some Ruby language construct or RoR framework construct that would enable me to implement this kind of design on an easier manner? Should I instead be thinking of many RoR applications somehow talking to each other? I really like RoR but I’m starting to find myself on a tough situation dealing with evolving mid-to-large systems (think 50+ database tables and 8+ sub-systems). I need to come up with a pattern that would force me to implement and design code that works and is maintainable on a long-term vision, however I’m not sure if this is because I don’t know the 100% of what the language and framework has to offer, or if I am just using it the wrong way (or both? :-). Comments? Thanks, Seb ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 4, 2009, 4:34am UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/2 "2009-02-04T04:34:28Z")
Datamapper. Blog: [http://random8.zenunit.com/](http://random8.zenunit.com/) Learn rails: [http://sensei.zenunit.com/](http://sensei.zenunit.com/) ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 4, 2009, 7:29pm UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/3 "2009-02-04T19:29:10Z")
Hi Julian, Thanks for your answer. I’ve seen Datamapper before. However, the way I understand it, Datamapper is pretty much just a replacement for ActiveRecord, so I don’t see how it would add the extra layer of abstraction I’m searching for… Did I miss something here? Thanks Seb ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 4, 2009, 7:46pm UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/4 "2009-02-04T19:46:15Z")
Hello Seb, An approach that I have used is to place the higher level business logic in model objects that do not inherit from ActiveRecord. In the way I think about larger systems, the higher level business logic is still part of the model. The model is not limited to managing the persistence of state. I don’t have a formal way of organizing these subsystem model objects as I haven’t tackled any projects that sound as extensive as what you are working on. HTH Kim On Feb 4, 2009, at 11:28 AM, sbrocher wrote: > > > high- > > > example, a credit card gateway, an accounting system, Fedex, you > > > The controllers do not have access to Models either. Instead, they > > > underlying database structure". > > > database > > > rest of the app would continue to use the same API calls to the > > > that would enable me to implement this kind of design on an easier > > > me to implement and design code that works and is maintainable on a > > > > - Show quoted text - – Kim S. - principal, Shrier and Deihl - [mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Remote Unix Network Admin, Security, Internet Software Development Tinker Internet Services - Superior FreeBSD-based Web Hosting [http://www.tinker.com/](http://www.tinker.com/) ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 4, 2009, 7:49pm UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/5 "2009-02-04T19:49:48Z")
A good starting point is read Eric Evan’s “Domain Driven Design”, you will probably learn a lot about how to organize big systems in any language. The book is easy to read and has examples in Java. - Maurício Linhares [http://alinhavado.wordpress.com/](http://alinhavado.wordpress.com/) (pt-br) | [http://blog.codevader.com/](http://blog.codevader.com/) (en) ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 5, 2009, 1:35am UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/6 "2009-02-05T01:35:05Z")
The reasons you explained you wanted the layer made me think you only needed datamapper. Be simpler rather than complex. Explain again why you need the layer, please? Remember YAGNI. Blog: [http://random8.zenunit.com/](http://random8.zenunit.com/) Learn rails: [http://sensei.zenunit.com/](http://sensei.zenunit.com/) ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 5, 2009, 10:07am UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/7 "2009-02-05T10:07:20Z")
Hi Julian, No worries. I’m just after the basic high-level design concept where you first break the (large) problem into several subsystems (i.e.: divide and conquer). Then define APIs for each subsystem. Then implement each subsystem. Test each system separately. Integrate. Test whole system. Also known as the “V” model at another level of abstraction. This has many benefits and is a proven technique to design large systems. It reduces coupling and makes it easier to integrate with other systems in the future, work with large teams, write more maintainable code, etc. It also enables you to break down the app onto different servers in the future as needed, by adding something like SOAP, REST or XML-RPC in between those APIs. For example, if a part of the app deals with inventory management, it will have it’s own API. Then if one day I decide to buy an inventory management system from a vendor that has its own API and similar features, all I have to do is write a connector (proxy) and place it inside my app, replacing the inventory management subsystem implementation by the proxy that communicates back and forth with the newly acquired system, but without needing to change any of my interface code, other business logic code, etc. Seb ---
**Author:** ![sbrocher](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sbrocher](https://www.ruby-forum.com/u/sbrocher)\ **Post date:** [February 5, 2009, 4:28pm UTC](https://www.ruby-forum.com/t/large-ror-systems-design-and-implementation/159388/8 "2009-02-05T16:28:38Z")
You may be better off using the new engines or merb slices Blog: [http://random8.zenunit.com/](http://random8.zenunit.com/) Learn rails: [http://sensei.zenunit.com/](http://sensei.zenunit.com/)