As we know the model can associate other model through the foreign key which is assigned or with an “_id” suffix by default. But can we define functional foreign key by ourselves ?
eg:
class Condition < ActiveRecord::Base
belongs_to :city_info, foreign_key: "substring_index(the_city,',',1)" end
class CityInfo < ActiveRecord::Base
end
>> Condition.includes(:city_info).references(:city_info).last
>> Mysql2::Error: Unknown column 'conditions.substring_index(the_city,',',1)' in 'on clause': SELECT ..... ......`conditions`.`substring_index(the_city,',',1)` ORDER BY `conditions`.`id` DESC LIMIT 1
It’s wrong. How can we achieve this.
I want to retrieve many conditions object, each associates with its first city_info by ActiveRecord with generating a single sql (not n+1
) like this:
select * from conditions left outer join city_info on convert(substring_index(conditions.the_city,',',1), unsigned integer) = city_info.id
ref: https://github.com/rails/rails/issues/14481
