Redmine

Hello Hubert,
I you need to patch the Project model by doing something such as:

plugins/my_plugin/init.rb:

require 'redmine'

Rails.configuration.to_prepare do
     require_dependency 'my_plugin/patches/project_patch'
end
[...]

plugins/my_plugin/lib/my_plugin/patches/project_patch.rb:

module MyPlugin
  module Patches
    module ProjectPatch
      def self.included(base) # :nodoc:

        base.send(:include, InstanceMethods)

        base.class_eval do
          unloadable # Send unloadable so it will not be unloaded in development
          has_many :your_model_plural_here, :dependent => :delete_all
          #If you need your code to run the destroy method, use ":dependent => :destroy" instead
        end
      end

      module InstanceMethods
          #Add methods to the Project class here
      end
    end
  end
end
Project.send(:include, MyPlugin::Patches::ProjectPatch)

This is a dynamic/clean patch of Project. It's always a bad idea to edit Redmine's core files.
Note that you need to restart your web server for the patch to be applied, even in development environment.
Tell me how it goes.
Cheers,