Question

How do I set up a belongs_to :through (which I know is not valid) relationship? For instance: A company has many departments. A department has many teams. And some teams are cross-functional so they can span many departments (habtm).

class Company < ActiveRecord::Base
  has_many :departments
  has_many :teams, through: :departments
end

class Department < ActiveRecord::Base
  belongs_to :company;
  has_and_belongs_to_many :teams
end

class Team < ActiveRecord::Base
  has_and_belongs_to_many :departments
end

How do I get company from team. What is a good way to do this? The first should work but can I or should I be trying to do it in the model as a relationship?

class Team < ActiveRecord::Base
  has_and_belongs_to_many :departments

  def company 
    departments.first.company
  end

end

or

class Team < ActiveRecord::Base
  has_and_belongs_to_many: departments

  has_one :company, through: departments  (<-- is this valid?, seems like this should be has_many but that's not right!)
end

Answer 1

The relationship you want is already there. If you know all the departments belong to the same company you can do

my_team.departments.first.company