如何在所有模型实例中获取所有has_many对象？

Question

I have the Event model. It has_many :participants .

Can do Event.all.each do |event| and then try to manipulate event.participants

But is there an easier way to get all participants for all events?

It's a typical problem in OO when you get an Array of "Events" back not an EventArray with the right methods.

Answer 1

You can get Participants that are part of any Event like this

Participant.where(event_id: Event.pluck(:id))

or just

Participant.all

if there are no Participants without an associated Event

Answer 2

Participant.joins(:event)应该让你参与一个活动。

Answer 3

Event.joins(:participants).select("participants.*")这将为所有与事件相关联的参与者提供

Answer 4

you can use eager_load and group_by in this issue. In your case

event = Event.eager_load(:participants).group_by(&:participants)

it will create a Hash of all events with associated participants. you can access 0 index for participants and 1 index for that event. Something like

event.first[0] = all the participants of that event
event.first[1] = that event