gistfile1.rb

# worker model
belongs_to :project1, :class_name => "Project", :foreign_key => "project1_foreign_key_name_in_workers_table"
belongs_to :project2, :class_name => "Project", :foreign_key => "project2_foreign_key_name_in_workers_table"
belongs_to :project3, :class_name => "Project", :foreign_key => "project3_foreign_key_name_in_workers_table"

# The project model is going to be harder, and you're not going to be
# able to intuitively assign workers to projects, but you can at least
# fudge-together some helper methods to make it look like you're
# leveraging the power of Rails! :-)

#project model
has_many :project1_keyed_workers, :class_name => "Worker", :foreign_key => "project1_foreign_key_name_in_workers_table"
has_many :project2_keyed_workers, :class_name => "Worker", :foreign_key => "project2_foreign_key_name_in_workers_table"
has_many :project3_keyed_workers, :class_name => "Worker", :foreign_key => "project3_foreign_key_name_in_workers_table"

def workers
 # build and array of all the arrays of workers, flatten it and get rid of nil values
 ([] << project1_keyed_workers << project2_keyed_workers << project3_keyed_workers).flatten.compact
end