RailsPlugins.org

Mongoid 2.0.0.beta6 gem's gemspec file specifies activemodel version to be 3.0.0.beta3. So in order to install Rails 3.0.0beta4, I manually changed it to be >= 3.0.0.beta3 because otherwise Bundler doesn't install Rails 3.0.0beta4. But when I actually tried to run specs (Rspec), error occurred that constant Mongoid not found.

Looking at GitHub, mongoid.gemspec has been modified about one hour ago and now it specifies ~>3.0.0.beta. Maybe we have to install mongoid from GitHub.

master branch is already rails3 compatible

please make sure to install it from github like this in Gemfile
gem "mongoid", :git => "git://github.com/durran/mongoid.git"
and change rails to beta2 in the line
gem "rails", "3.0.0.beta2"

Gemfile:
gem "mongoid", :git => "git://github.com/durran/mongoid.git", :branch => "prerelease"
gem "mongo"
gem "mongo_ext", :require => nil