how to select fields from joined table properly? - ruby-on-rails

Question

Here are my simplified models, I have joined models:
class Apartment < ApplicationRecord
has_many :towers
end
and
class Tower < ApplicationRecord
belong_to :apartment
end
and then I tried to join both tables in controller. I also tried it in rails console like this :
Apartment.joins(:towers).select('apartments.id', 'apartments.name', 'towers.id' , 'towers.name')
the problem is above query only returns
apartments.id and apartments.name
also tried to use alias like this, still no luck
Apartment.joins(:towers).select('apartments.id', 'apartments.name',
'towers.id as towerid' , 'towers.name as towername')
I have confirmed that all towers have an apartment, I know i could do this to get 1 record
Apartment.joins(:towers).select('apartments.id', 'apartments.name',
'towers.id' , 'towers.name').first.towers.id
and etc, but i need all records and all those fields, please advice.
here is the latest result i got in rails console :
Apartment Load (1.0ms) SELECT apartments.id, apartments.name, towers.id as towerid, towers.
tower_name as towername FROM `apartments` INNER JOIN `towers` ON `towers`.`apt_id` = `
apartments`.`id`
=> #<ActiveRecord::Relation [#<Apartment id: 5, name: "basura">, #<Apartment id: 5, apt_
name: "basura">, #<Apartment id: 124, name: "hydra">, #<Apartment id: 124, name: "hy
dra">, #<Apartment id: 126, name: "mediterania">, #<Apartment id: 126, name: "mediterania">, #<Apartment id: 142, name: "apartement gajah mada">, #<Apartment id: 142, name: "apartement gajah mada">]>
as you can see, above query only return 2 fields, i need the result to be like this :
#<Apartment id: 126, name: "mediterania", tower_id: 12, tower_name: "tower A">,
#<Apartment id: 126, name: "mediterania", tower_id: 15, tower_name: "tower F">
etcc...

Answer 1

The only way I see this is possible is using as
q = Apartment.joins(:towers).select('apartments.id, apartments.name, towers.id as t_id, towers.name as t_name')
q.first.t_id
q.first.t_name
Why first.towers.id will not work?
apartment.towers will return ActiveRecord::Associations::CollectionProxy. You can think of it as a collection of towers. In SQL query you are referring to towers table. But when you run apartment.towers.id you are calling id on CollectionProxy object which will not work. You can get first tower using towers.first.
Regarding,
Apt Load (1.0ms) SELECT apts.id, apts.apt_name, towers.id as towerid, towers.
tower_name as towername FROM `apts` INNER JOIN `towers` ON `towers`.`apt_id` = `
apts`.`id`
=> #<ActiveRecord::Relation [#<Apt id: 5, apt_name: "basura">, #<Apt id: 5, apt_
name: "basura">, #<Apt id: 124, apt_name: "hydra">, #<Apt id: 124, apt_name: "hy
dra">, #<Apt id: 126, apt_name: "mediterania">, #<Apt id: 126, apt_name: "mediterania">, #<Apt id: 142, apt_name: "apartement gajah mada">, #<Apt id: 142, apt_name: "apartement gajah mada">]>
What you see in console is result returned by inspsect method. The inspect method is not designed to show non column attributes. Hence even if you have towername in memory it will only show attributes which are columns of Apartment model.
More about inspect
I also recommend to try following:
Apartment.joins(:towers).pluck('apartments.id, apartments.name, towers.id as t_id, towers.name as t_name')
Above statement will get all data in array. The same result you get with select but select will not load all data in array.

Answer 2

You should use
Apartment.joins(:towers).select('apartments.id, apartments.name, towers.id , towers.name')
that is all column names inside a single string.
Refer this.

Answer 3

Rails 7 adds support for such queries, now select accepts hash
You can use aliases like this
Apartment
.joins(:towers)
.select(
apartments: { id: :apartment_id, name: :apartment_name },
towers: { id: :tower_id, name: :tower_name }
)
It produces such query
SELECT apartments.id AS apartment_id, apartments.name AS apartments_name,
towers.id AS tower_id, towers.name AS tower_name
FROM apartments
INNER JOIN towers ON towers.apartment_id = apartments.id

Answer 4

You can try the alias names like below
Apartment.joins(:towers).select('apartments.id as apartment_id, apartments.name as apartment_name, towers.id as tower_id , towers.name as tower_name)

Answer 5

You can try this
Apartment.joins(:towers).select('apartments.id as id, apartments.name as apartment_name, towers.id as tower_id , towers.name as tower_name)
you will get the response like this
#ActiveRecord::Relation [#<Apt id: 126, apt_name: "mediterania", tower_id: 12, tower_name: "tower A">,
#<Apt id: 126, apt_name: "mediterania", tower_id: 15, tower_name: "tower F">]>