As a Rails developer, I used to directly map my business models into code within AR instances but as the number of models grows, it become difficult to have a clear idea of the whole picture.

I discovered rails-erd gem and started to use it intensively to have a snapshot of the models relations and associations inside the app by generating an ERD from your models.

rails-erd automatically generates a PDF with your app models graph using graphviz library.

Here's how to use it

Installation

Install graphviz (if not yet)

sudo apt-get install graphviz

Add the gem

In the project gemfile add

group :development do
  gem 'rails-erd'
end

Then execute cd PATH_OF_THE_PROJECT && bundle install

Using it

It's as simple as a bundle exec rake erd and it will generate a PDF file in the root of the app.

See what it can do here in the erd gallery