Question

Given a model Event which

has_many :user_events

And a model UserEvent which

belongs_to :event

I could get the related user_events from a single event object, like so:

event = Event.find(1)
user_events = event.user_events

But is there an equivalent relation accessor for a collection of events? For example:

events = Event.where(:event_type => 'fun')
user_events = events.user_events

Which would return the user_events which belong to any ‘fun’ events using something like.

SELECT user_events.* FROM user_events JOIN events on (events.id = user_events.event_id) where (events.event_type = 'fun');

Answer 1

No, there isn’t a relation accessor for a collection of events.

In the meantime, you can do:

events = Event.includes(:user_events).where(:event_type => 'fun')
user_events = events.map(&:user_events).flatten

The user_events are eager loaded thanks to includes(:user_events). That’s commonly used.

We use the same logic when we do things like that (simplified):

# controller
@posts = Post.includes(:comments)

# view
<% @post.each do |post| %>
  # display your post
  <% post.comments.each do |comment| %>
    # display each comment
  <% end %>
<% end %>