[Ror-es] Duda sobre foreign keys

[Jose Ferrer]

Tengo una tabla con ofertas de coches:

car_offers (id, make_id, model_id...)

Y otra con marcas de coches:

makes (id, name)

Mi pregunta es que tengo que hacer exactamente para, al listar, poder  
poner @car_offers.make.name porque obtengo el error este:

Mysql::Error: Unknown column 'makes.car_offer_id' in 'on clause':  
SELECT car_offers.`id` AS t0_r0, car_offers.`make_id` AS t0_r1,  
car_offers.`model` AS t0_r2, car_offers.`kilometers` AS t0_r3,  
car_offers.`power_in_kw` AS t0_r4, car_offers.`registration_date` AS  
t0_r5, car_offers.`price` AS t0_r6, car_offers.`car_body_id` AS  
t0_r7, car_offers.`car_type_id` AS t0_r8, car_offers.`fuel_id` AS  
t0_r9, car_offers.`transmission_id` AS t0_r10, car_offers.`color_id`  
AS t0_r11, car_offers.`door_id` AS t0_r12, car_offers.`cushion` AS  
t0_r13, car_offers.`further_vehicle_information` AS t0_r14,  
car_offers.`contact_name` AS t0_r15, car_offers.`contact_telephone`  
AS t0_r16, car_offers.`contact_mobile` AS t0_r17,  
car_offers.`contact_email` AS t0_r18, makes.`id` AS t1_r0,  
makes.`name` AS t1_r1 FROM car_offers  LEFT OUTER JOIN makes ON  
makes.car_offer_id = car_offers.id


Por otro lado, si en el modelo pongo esto:

class CarOffer < ActiveRecord::Base
has_one     :make,
			:class_name => "CarOffer",
			 :foreign_key => "make_id"




Obtengo el siguiente error:

You have a nil object when you didn't expect it!
The error occured while evaluating nil.name
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