具有嵌套关联和组的Rails查询（按关联对象）

Question

Given this model relationships:

orders.rb
belongs_to user

user.rb
belongs_to company

company.rb
has_many users

I wanted to count all orders made by each company, so I got this:

Order.joins(user: :company)
.group(['companies.name, companies.id])
.count

and the result is

["Company 1", 1] => 123

BUT I don't know how to change this query to have

<Company id: 1,name: "Jim Beam"> => 5

instead of array of Company's attributes.

Answer 1

This can be made easier by adding another association to the model:

# company.rb
has_many :users
has_many :orders, through: :users

Then you can do this:

   companies = Company.
               joins(:orders).
               group("company.id").
               select("company.id, company.name, count(orders.id) as orders_count")

if you then say companies.first you will see something like this:

#<Company:0x005610fa35e678 id: 15 name: 'foo'>

it doesn't look like the orders_count is there. But it actually has been loaded already. You can get at it like this:

companies.first.orders_count

You can also see it if you convert the company to a hash:

companies.first.attributes # => { id: 15, orders_count: 2, name: "foo" }

In Postgres at least, if you want to get more data in the attributes hash you have to individually specify each of the columns in the select string. I'm not sure about other databases.