从集合中获取所有ID

Question

I got my collection items like this :

hotels = Hotel.where('selection = ?', 1).limit(4)

How can I get all ids of this items without a loop? Can i use something like :

hotels.ids ? 

Thank you

Answer 1

What about trying hotels.map(&:id) or hotels.map{|h| h.id } hotels.map{|h| h.id } ?

They both mean the same thing to Ruby, the first one is nicer to accustomed ruby-ists usually, whilst the second one is easier to understand for beginners.

Answer 2

If you only need an array with all the ids you should use pluck as it makes the right query and you don't have to use any ruby. Besides it won't have to instantiate a Hotel object for each record returned from the DB. (way faster).

Hotel.where(selection: 1).pluck(:id)
# SELECT hotels.id FROM hotels WHERE hotels.selection = 1
# => [2, 3]

Answer 3

If you are using Rails > 4, you can use the ids method:

Person.ids  # SELECT people.id from people

More info: http://apidock.com/rails/ActiveRecord/Calculations/ids

Answer 4

你也可以只拉出id。

hotels.select(:id).where(selection: 1)