Question

I am working on the project and now I need to add a foreign key. I have these two models:class

class Owner < ActiveRecord::Base
  has_many :shops
end

class Shop < ActiveRecord::Base
  belongs_to :owner
  has_many :cities
end

class City < ActiveRecord::Base
  belongs_to :shop, :foreign_key => 'shop_sid'
end

My goal is print all cities, in which is the shop. I am trying to do that this way:

<% @owner.shops.each do |shop| %>
  <% shop.cities.each do |city| %>
     <%=city.position%><br />
  <%end%>
<%end>

But I am getting the error
PG::Error: ERROR:  column cities.shop_id does not exist
LINE 1: ...T "cities".* FROM "cities"  WHERE "cities...
                                                             ^
: SELECT "cities".* FROM "cities"  WHERE "cities"."shop_id" = 8

I also tried to add the foreign key to the cities table:

alter table cities add foreign key (shop_sid) references shops (sid);

But got

ERROR:  there is no unique constraint matching given keys for referenced table "shops"

How could I solve this problem about foreign key? Or, would be also better to update the associations?

EDIT – error message:

PG::Error: ERROR:  operator does not exist: character varying = integer
LINE 1: ...ons"  WHERE "cities"."shop_sid" = 1034
                                                                 ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
: SELECT "cities".* FROM "cities"  WHERE "cities"."shop_sid" = 1034

Answer 1

You need to specify the foreign key on each side of the relation:

class Shop < ActiveRecord::Base
  belongs_to :owner
  has_many :cities, :foreign_key => 'shop_sid'
end

class City < ActiveRecord::Base
  belongs_to :shop, :foreign_key => 'shop_sid'
end