Rails 3 scopes with HABTM (has and belongs to many) relations
There are already many posts about this, but maybe this simple example will help you understand this subject even better. # First model: tag.rb # note that pomodori is a custom plural for pomodoro class Tag < ActiveRecord::Base has_and_belongs_to_many :pomodori end # Second model: pomodoro.rb # here is how to define a Rails 3 scope through the join table: class Pomodoro < ActiveRecord::Base has_and_belongs_to_many :tags scope :by_tag, lambda { |tag_text| joins("join pomodori_tags, tags")....