Dynamic "OR" conditions in Rails 3

I am working on a carpool application where people can search for lifts. They should be able to select the city from which they would liked to be picked up and choose a radius which will then add the cities in range to the query. However the way it is s开发者_StackOverflow中文版o far is that i can only chain a bunch of "AND" conditions together where it would be right to say "WHERE start_city = city_from OR start_city = a_city_in_range OR start_city = another_city_in_range"

Does anyone know how to achive this? Thanks very much in advance.

class Search < ActiveRecord::Base

def find_lifts    
  scope = Lift.where('city_from_id = ?', self.city_from)
  #returns id of cities which are in range of given radius
  @cities_in_range_from = City.location_ids_in_range(self.city_from, self.radius_from)
  #adds where condition based on cities in range
  for city in @cities_in_range_from
    scope = scope.where('city_from_id = ?', city)
    #something like scope.or('city_from_id = ?', city) would be nice..          
  end
end

You can use "IN" operator instead of "=" without using SQL syntax With Arel (used by Rails 3.0) you can do that this way

class Search < ActiveRecord::Base

  def find_lifts    

    #returns id of cities which are in range of given radius
    @cities_in_range_from = City.location_ids_in_range(self.city_from, self.radius_from)
    scope =  Lift.where{ :city_from_id => [self.city_from] + @cities_in_range_from })

    # ... and so on
  end
end