Ask HN: How can I learn "advanced" data modelling for Rails?

I'm a beginner (hobbyist) Rails developer. I've gone through many of the available tutorials, such as Michael Hartl's excellent Ruby on Rails Tutorial at http://ruby.railstutorial.org/ (both editions, books, and screencasts). I can build and understand simple CRUD-type applications with associations with no problems.

Now, I want to "scratch my own itch" and build an application I can actually use in my work. Basically, it will need to be able to keep track of tasks and comments arranged as projects and project templates. I'm running into difficulty designing these models and associations because they are more complex. I'm sure I could find or buy an application to do this, but I'd really like to learn how to do it myself, instead.

Question: Are there techniques or resources (books, tutorials, articles) or forums where I can learn to design more complex models and associations? This doesn't seem like it's specific to Rails (to me). Should I be researching database techniques, models, associations, for example, to get ideas?