ruby on rails - Using OR with queries in a scope

Question

In Rails3 I have:

Class Teacher
  #  active                 :boolean
  has_and_belongs_to_many :subjects

Class Subject
  #  active                 :boolean
  has_and_belongs_to_many :teachers

I am trying to construct a Teacher scope that returns all Teachers that are active or are associated with a Subject that is active.

These scopes work individually, but how to combine them as a single scope with an OR?

scope :active_teachers, where(active: true)
scope :more_active_teachers, joins(:subjects).where(:subjects => {active: true})

I've tried this without success:

scope :active_teachers, where(active: true).or(joins(:subjects)
      .where(:subjects => {active: true}))

UPDATE:

I thought I had a solution, but this no longer lazy loads, hits the database twice and — most importantly — returns an array rather than an AR object!

scope :active_teachers, where(active: true) |
                        joins(:subjects).where(:subjects => {active: true})

Answer 1

You have Squeel to your rescue. More details here.

Using that, you could define something like:

class Teacher
  ...
  scope :active_teachers, joins{subjects}.where {(active == true) | (subjects.active == true)}
  ...
end