内部联接选择多列

Question

如果我提交

Role.select("roles.character, actors.lname AS actors_lname").joins(:actor)

它returns:

Role Load (0.0ms) SELECT roles.character, actors.lname AS actors_lname 
FROM "roles" INNER JOIN "actors" ON "actors"."id" = "roles"."actor_id"
#<ActiveRecord::Relation [#<Role id: nil, character: "Ellis Boyd 'Red' Redding">, 
#<Role id: nil, character: "Andy Dufresne">, #<Role id: nil, character: "Warden Norton">]>

为什么不显示 actors.lname 列？

Answer 1

使用select.

Order.select("orders.id, customers.name").joins(:customers)

如果你为它们取别名，你可以获取关联的值

orders = Order.select("orders.id, customers.name AS customer_name").joins(:customers)

# you must call the method implicitly, or use .attributes
orders.first.customer_name

请注意，customer_name 的值不会出现在记录检查中。因此下面的代码

orders.first

在 IRB 中不会打印出属性。

内部联接选择多列

Inner joins selecting multiple columns

ruby-on-rails

rails-activerecord