Question

I have a fairly conventional Grails application. It’s monolithic; although it’s somewhat split into plugins along functionality lines, it is built into a single war for deployment. Due to company architectural constraints, I need to consider isolating the app’s persistence into a web service (or series of web services). What’s the best approach to dividing a Grails application into a persistence service and a presentation application?

Answer 1

I don’t have an out-of-the-box solution for your problem, and I don’t believe there is one. I’ll just explain the solution I use and what I would consider in your case.

In my organisation, our approach is to separate our applications in a Grails back-end and a front-end in Flex. The reason is that we have many ready-to-use Flex components that would take too much time to re-implement using pure web technologies, but here’s not my point.

Creating a REST back-end in Grails is quick, as views are scaffolded when appropriate, controllers are straightforward, and input validation is greatly simplified by Domain constraints.

The drawback of this split is that definition of domain objects have to be duplicated in the front-end. You might includes objects validation in the front-end or not, but if you omit them, it will have an influence on UI responsiveness (requests to the REST back-end in AJAX calls for real-time validation to get the errors). At the end, our application is quite cumbersome because modifying objects in the back-end implies modification in the front-end. Furthermore, we do validation in both the front-end AND the back-end, and this code is not shared, so it must stay in phase and maintained at two places.

Our applications are split in a way that’s similar to two completely distinct Grails applications that would share no code. A solution that would work in your case but is not what you are looking for, for sure.

In your case, I see two viable solutions for the web front-end:

• use the Groovy REST client library to fetch and send back your domain objects directly from your controller. If needed, pack them in command objects that reflect your domain objects, so that you can share validation code with the back-end.

• create some kind of REST GORM that replaces Hibernate with queries to your REST web service. You could look at the GORM for Mongo Plugin as an example of how to create such a GORM replacement.

I like the last idea, it would be a useful public plug-in. It doesn’t exist yet, unfortunetly.