sms-pager/app/models/child.rb

class Child < ActiveRecord::Base
  has_many :parenthoods
  has_many :parents, through: :parenthoods, source: :person

  validates :first_name, presence: true
  validates :last_name, presence: true

  scope :not_related_to, lambda { |parent_id|
    joins("LEFT JOIN (
          SELECT child_id
          FROM parenthoods
          WHERE person_id = #{sanitize(parent_id)}
        ) as s1 on s1.child_id = children.id")
      .where("s1.child_id is null")
      .order(:first_name, :last_name)
      .uniq
  }

  def name
    "#{first_name} #{last_name}"
  end
end